diff --git a/src/main/java/model/User.java b/src/main/java/model/User.java
index 28590b2..a5d7ed3 100644
--- a/src/main/java/model/User.java
+++ b/src/main/java/model/User.java
@@ -3,41 +3,59 @@
 import password.PasswordHash;
 
 public class User {
-  private final String userName;
-  private final String phoneNumber;
+  private String userName;
+  private String phoneNumber;
   private final String eMail;
-  private final PasswordHash password;
+  private String password;
 
-  public User(String userName, String phoneNumber, PasswordHash password, String eMail) {
+  public User(String userName, String phoneNumber, String password, String eMail) {
     this.userName = userName;
     this.phoneNumber = phoneNumber;
     this.eMail = eMail;
     this.password = password;
 
-    if ( userName == null || userName.isBlank() ) {
+    if (userName == null || userName.isBlank()) {
       throw new IllegalArgumentException("Username has to be filled in");
     }
 
-    if ( eMail == null || eMail.isBlank() ) {
+    if (eMail == null || eMail.isBlank()) {
       throw new IllegalArgumentException("E-mail has to be filled in");
     }
 
-    if ( phoneNumber == null || phoneNumber.isBlank() ) {
+    if (phoneNumber == null || phoneNumber.isBlank()) {
       throw new IllegalArgumentException("Phonenumber has to be filled in");
     }
 
-    if ( phoneNumber.length() != 8 ) {
+    if (phoneNumber.length() != 8) {
       throw new IllegalArgumentException("Fill in a phonenumber with 8 digits");
     }
   }
 
-  public String getUsername() { return userName; }
+  public String getUsername() {
+    return userName;
+  }
 
-  public String getPhoneNumber() { return phoneNumber; }
+  public String getPhoneNumber() {
+    return phoneNumber;
+  }
 
-  public String getEMail() { return eMail; }
+  public String getEMail() {
+    return eMail;
+  }
 
-  public PasswordHash getPasswordHash() { return password; }
+  public String getPassword() {
+    return password;
+  }
 
+  public void setPassword(String password) {
+    this.password = password;
+  }
 
-}
+  public void setUsername(String userName) {
+    this.userName = userName;
+  }
+
+  public void setPhonenumber (String phoneNumber) {
+    this.phoneNumber = phoneNumber;
+  }
+}
\ No newline at end of file
diff --git a/src/main/java/password/PasswordHash.java b/src/main/java/password/PasswordHash.java
index cda7ced..4faea00 100644
--- a/src/main/java/password/PasswordHash.java
+++ b/src/main/java/password/PasswordHash.java
@@ -19,7 +19,7 @@ public static String hash(String password) {
       }
     }
 
-    public static boolean mathches(String password, String hashedPassword) {
+    public static boolean matches(String password, String hashedPassword) {
       String newHash = hash(password);
       return newHash.equals(hashedPassword);
     }
diff --git a/src/main/java/register/UserRegister.java b/src/main/java/register/UserRegister.java
index 398cee3..92ce86a 100644
--- a/src/main/java/register/UserRegister.java
+++ b/src/main/java/register/UserRegister.java
@@ -1,6 +1,8 @@
 package register;
 
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import model.User;
 
@@ -17,4 +19,16 @@ public void addUser(User user) {
       users.put(user.getUsername(), user);
     }
   }
+
+  public void removeUser(User user) {
+    if (users.containsValue(user)) {
+      users.remove(user);
+    }
+  }
+
+  public List<User> getAllUsers() {
+    return new ArrayList<>(users.values());
+  }
+
+  public int numberOfAuthors() { return users.size(); }
 }
diff --git a/src/main/java/service/AuthService.java b/src/main/java/service/AuthService.java
index c60b35e..3e0f07b 100644
--- a/src/main/java/service/AuthService.java
+++ b/src/main/java/service/AuthService.java
@@ -1,4 +1,16 @@
 package service;
 
+import model.User;
+import password.PasswordHash;
+
 public class AuthService {
+
+  public User register(String userName, String eMail, String password, String phoneNumber) {
+    String hashedPassword = PasswordHash.hash(password);
+    return new User(userName, phoneNumber, hashedPassword, eMail);
+  }
+
+  public boolean login(User user, String password) {
+    return PasswordHash.matches(password, user.getPassword());
+  }
 }
diff --git a/src/main/java/service/UserService.java b/src/main/java/service/UserService.java
index 467d401..8590544 100644
--- a/src/main/java/service/UserService.java
+++ b/src/main/java/service/UserService.java
@@ -1,4 +1,23 @@
 package service;
 
+import model.User;
+import register.UserRegister;
+import password.PasswordHash;
+import service.AuthService;
+
+
 public class UserService {
+  private AuthService authService;
+
+  public UserService() {
+    this.authService = authService;
+  }
+
+  public boolean changeUsername(User user, String password, String newUsername) {
+    if (authService.login(user, password)) {
+      user.setUsername(newUsername);
+      return true;
+    }
+    return false;
+  }
 }