diff --git a/MailSystem/src/domain/UserManager.java b/MailSystem/src/domain/UserManager.java
index 7d6ee2b..b796fd0 100644
--- a/MailSystem/src/domain/UserManager.java
+++ b/MailSystem/src/domain/UserManager.java
@@ -5,11 +5,13 @@ import java.util.ArrayList;
 import java.util.Arrays;
 
 import domain.exception.UserAlreadyExistsException;
+import domain.exception.UserNotFoundException;
 
 public class UserManager {
 
     private ArrayList<User> users;
-
+    private User currentUser;
+    
     public UserManager() {
         this.users = new ArrayList<>();
     }
@@ -31,10 +33,8 @@ public class UserManager {
             throw new IllegalArgumentException("Passwords do not match!");
 
         String email = username + "@easymail.de";
-
-        for (User tempUser : users) 
-            if (tempUser.getUsermail().getUsername().equalsIgnoreCase(email)) 
-                throw new UserAlreadyExistsException("This email address is already taken!");
+        if (findUserByUsername(email) != null)
+        	throw new UserAlreadyExistsException("This email address is already taken!");
 
         int month = getMonthNumber(monthName);
         if (month == 0) 
@@ -63,8 +63,64 @@ public class UserManager {
         Arrays.fill(password, ' ');
         return false;
     }
+    
+    public boolean removeUser(String username) throws UserNotFoundException {
+        if (username == null || username.trim().isEmpty()) 
+            throw new IllegalArgumentException("Username cannot be null or empty!");
+        
+        User userToBeRemoved = findUserByUsername(username);
+        if (userToBeRemoved == null) 
+            throw new UserNotFoundException("This email address is not found!");
+        
+        users.remove(userToBeRemoved);
+        return true;
+    }
 
+    public int getNumberOfUsers() {
+    	return users.size();
+    }
+    public boolean updateUser(String username, String firstName, String lastName, char[] password, char[] confirm) throws Exception {
+        User userToBeUpdated = findUserByUsername(username);
+        if (userToBeUpdated == null)
+            throw new UserNotFoundException("This email address is not found!");
 
+        if (firstName == null || lastName == null || password == null || confirm == null)
+            throw new IllegalArgumentException("Fields cannot be null!");
+
+        if (firstName.trim().isEmpty() || lastName.trim().isEmpty())
+            throw new IllegalArgumentException("First name and last name are required!");
+
+        if (!Arrays.equals(password, confirm))
+            throw new IllegalArgumentException("Passwords do not match!");
+
+        userToBeUpdated.setFirstname(firstName);
+        userToBeUpdated.setLastname(lastName);
+        
+        char[] passwordCopy = Arrays.copyOf(password, password.length);
+        userToBeUpdated.getUsermail().setPassword(passwordCopy);
+        Arrays.fill(password, ' ');
+        Arrays.fill(confirm, ' ');
+
+        return true;
+    }
+
+    public User getUserByUsername(String username) {
+    	this.currentUser = findUserByUsername(username);
+    	if (this.currentUser == null)
+    		return null;
+    	
+		return currentUser;
+	}
+    
+    private User findUserByUsername(String username) {
+    	for (User tempUser : users)
+    		if (tempUser.getUsermail().getUsername().equalsIgnoreCase(username))
+    				return tempUser;
+    	
+    	return null;
+    }
+    
+    
     private int getMonthNumber(String txtMonth) {
         switch (txtMonth.toLowerCase()) {
             case "januar": return 1;
@@ -82,5 +138,7 @@ public class UserManager {
             default: return 0;
         }
     }
+
+	
 }
 
diff --git a/MailSystem/src/domain/exception/UserNotFoundException.java b/MailSystem/src/domain/exception/UserNotFoundException.java
new file mode 100644
index 0000000..d0fc3a4
--- /dev/null
+++ b/MailSystem/src/domain/exception/UserNotFoundException.java
@@ -0,0 +1,7 @@
+package domain.exception;
+
+public class UserNotFoundException extends Exception {
+	public UserNotFoundException(String error) {
+		super(error);
+	}
+}
diff --git a/MailSystem/src/domain/unitTest/RemoveUserTest.java b/MailSystem/src/domain/unitTest/RemoveUserTest.java
new file mode 100644
index 0000000..ab6d186
--- /dev/null
+++ b/MailSystem/src/domain/unitTest/RemoveUserTest.java
@@ -0,0 +1,48 @@
+package domain.unitTest;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import domain.UserManager;
+import domain.exception.UserNotFoundException;
+
+class RemoveUserTest {
+
+    private UserManager userManager;
+
+    @BeforeEach
+    void setUp() throws Exception {
+        userManager = new UserManager();
+        userManager.addUser("Jane", "Doe", "janedoe", 1992, 20, "April", "securePass1".toCharArray(), "securePass1".toCharArray());
+    }
+
+    @Test
+    void testRemoveUserSuccessfully() throws Exception {
+        boolean removed = userManager.removeUser("janedoe@easymail.de");
+        assertTrue(removed);
+
+        assertNull(userManager.getUserByUsername("janedoe@easymail.de"));
+    }
+
+    @Test
+    void testRemoveUserNotFound() {
+        assertThrows(UserNotFoundException.class, () -> {
+            userManager.removeUser("nonexistent@easymail.de");
+        });
+    }
+
+    @Test
+    void testRemoveUserNullUsername() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.removeUser(null);
+        });
+    }
+
+    @Test
+    void testRemoveUserEmptyUsername() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.removeUser("   ");
+        });
+    }
+}
+
diff --git a/MailSystem/src/domain/unitTest/UpdateUserTest.java b/MailSystem/src/domain/unitTest/UpdateUserTest.java
new file mode 100644
index 0000000..64bcd5f
--- /dev/null
+++ b/MailSystem/src/domain/unitTest/UpdateUserTest.java
@@ -0,0 +1,130 @@
+package domain.unitTest;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import domain.User;
+import domain.UserManager;
+import domain.exception.UserNotFoundException;
+
+class UpdateUserTest {
+
+    private UserManager userManager;
+
+    @BeforeEach
+    void setUp() throws Exception {
+        userManager = new UserManager();
+        userManager.addUser("John", "Doe", "johndoe", 1990, 15, "Mai", "password123".toCharArray(), "password123".toCharArray());
+    }
+
+    @Test
+    void testUpdateUserSuccessfully() throws Exception {
+        boolean updated = userManager.updateUser(
+            "johndoe@easymail.de", 
+            "Johnny", 
+            "Doeman", 
+            "newpass123".toCharArray(), 
+            "newpass123".toCharArray()
+        );
+        assertTrue(updated);
+        
+        User updatedUser = userManager.getUserByUsername("johndoe@easymail.de");
+        assertEquals("Johnny", updatedUser.getFirstname());
+        assertEquals("Doeman", updatedUser.getLastname());
+    }
+
+    @Test
+    void testUpdateUserNotFound() {
+        assertThrows(UserNotFoundException.class, () -> {
+            userManager.updateUser(
+                "unknown@easymail.de", 
+                "Johnny", 
+                "Doeman", 
+                "newpass123".toCharArray(), 
+                "newpass123".toCharArray()
+            );
+        });
+    }
+
+    @Test
+    void testUpdateUserNullFields() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                null, 
+                "Doeman", 
+                "newpass123".toCharArray(), 
+                "newpass123".toCharArray()
+            );
+        });
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "Johnny", 
+                null, 
+                "newpass123".toCharArray(), 
+                "newpass123".toCharArray()
+            );
+        });
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "Johnny", 
+                "Doeman", 
+                null, 
+                "newpass123".toCharArray()
+            );
+        });
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "Johnny", 
+                "Doeman", 
+                "newpass123".toCharArray(), 
+                null
+            );
+        });
+    }
+
+    @Test
+    void testUpdateUserEmptyFirstnameOrLastname() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "   ", 
+                "Doeman", 
+                "newpass123".toCharArray(), 
+                "newpass123".toCharArray()
+            );
+        });
+
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "Johnny", 
+                "    ", 
+                "newpass123".toCharArray(), 
+                "newpass123".toCharArray()
+            );
+        });
+    }
+
+    @Test
+    void testUpdateUserPasswordMismatch() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            userManager.updateUser(
+                "johndoe@easymail.de", 
+                "Johnny", 
+                "Doeman", 
+                "newpass123".toCharArray(), 
+                "differentpass".toCharArray()
+            );
+        });
+    }
+}