diff --git a/apigateway/src/main/java/vaultweb/apigateway/controller/GatewayAuthController.java b/apigateway/src/main/java/vaultweb/apigateway/controller/GatewayAuthController.java
index edb8af4..f624aa4 100644
--- a/apigateway/src/main/java/vaultweb/apigateway/controller/GatewayAuthController.java
+++ b/apigateway/src/main/java/vaultweb/apigateway/controller/GatewayAuthController.java
@@ -12,6 +12,7 @@
 import org.springframework.web.bind.annotation.RestController;
 
 import vaultweb.apigateway.dto.request.ChangePasswordRequest;
+import vaultweb.apigateway.dto.request.ChangeUsernameRequest;
 import vaultweb.apigateway.dto.request.LoginRequest;
 import vaultweb.apigateway.dto.request.UserRegistrationRequest;
 import vaultweb.apigateway.dto.response.AuthResponse;
@@ -60,9 +61,10 @@ public Mono<Void> logout() {
     return authService.logout();
   }
 
+  @ResponseStatus(HttpStatus.OK)
   @PostMapping("change-username")
-  public String changeUsername() {
-    return "changeUsername";
+  public Mono<Void> changeUsername(@Valid @RequestBody ChangeUsernameRequest request) {
+    return authService.changeUsername(request);
   }
 
   @PostMapping("change-email")
@@ -70,6 +72,7 @@ public String changeEmail() {
     return "changeEmail";
   }
 
+  @ResponseStatus(HttpStatus.OK)
   @PostMapping("change-password")
   public Mono<Void> changePassword(@Valid @RequestBody ChangePasswordRequest request) {
     return authService.changePassword(request);
diff --git a/apigateway/src/main/java/vaultweb/apigateway/dto/request/ChangeUsernameRequest.java b/apigateway/src/main/java/vaultweb/apigateway/dto/request/ChangeUsernameRequest.java
new file mode 100644
index 0000000..bf5f767
--- /dev/null
+++ b/apigateway/src/main/java/vaultweb/apigateway/dto/request/ChangeUsernameRequest.java
@@ -0,0 +1,6 @@
+package vaultweb.apigateway.dto.request;
+
+import jakarta.validation.constraints.NotEmpty;
+
+public record ChangeUsernameRequest(
+    @NotEmpty(message = "Your new username is required") String newUsername) {}
diff --git a/apigateway/src/main/java/vaultweb/apigateway/service/auth/AuthService.java b/apigateway/src/main/java/vaultweb/apigateway/service/auth/AuthService.java
index ce3aef0..daa6024 100644
--- a/apigateway/src/main/java/vaultweb/apigateway/service/auth/AuthService.java
+++ b/apigateway/src/main/java/vaultweb/apigateway/service/auth/AuthService.java
@@ -3,6 +3,7 @@
 import org.springframework.stereotype.Service;
 
 import vaultweb.apigateway.dto.request.ChangePasswordRequest;
+import vaultweb.apigateway.dto.request.ChangeUsernameRequest;
 import vaultweb.apigateway.dto.request.LoginRequest;
 import vaultweb.apigateway.dto.request.UserRegistrationRequest;
 import vaultweb.apigateway.dto.response.AuthResponse;
@@ -128,6 +129,41 @@ public Mono<Void> changePassword(ChangePasswordRequest request) {
             });
   }
 
+  public Mono<Void> changeUsername(ChangeUsernameRequest request) {
+    return securityContextUtil
+        .getAuthenticatedUsername()
+        .flatMap(userRepository::findByUsername)
+        .switchIfEmpty(
+            Mono.error(
+                new DefaultException(
+                    "username from token has no registered user",
+                    DefaultExceptionLevels.AUTHENTICATION_EXCEPTION)))
+        .flatMap(
+            user -> {
+              if (request.newUsername().equals(user.getUsername())) {
+                return Mono.error(
+                    new DefaultException(
+                        "You didn't change anything", DefaultExceptionLevels.DEFAULT_EXCEPTION));
+              }
+
+              return userRepository
+                  .existsByUsername(request.newUsername())
+                  .flatMap(
+                      usernameExists -> {
+                        if (usernameExists) {
+                          return Mono.error(
+                              new DefaultException(
+                                  "User with username "
+                                      + request.newUsername()
+                                      + " already exists"));
+                        }
+
+                        user.setUsername(request.newUsername());
+                        return userRepository.save(user).then();
+                      });
+            });
+  }
+
   public Mono<AuthResponse> switchToken(String token) {
     // find refresh
     return refreshTokenRepository
diff --git a/docker-compose.yml b/docker-compose.yml
index 4b6da8d..9306509 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -10,7 +10,7 @@ services:
       POSTGRES_PASSWORD: password
       POSTGRES_DB: auth_gateway_db
     ports:
-      - "5433:5432"
+      - "5432:5432"
     volumes:
       - postgres_data:/var/lib/postgresql/data