diff --git a/webseite/classes/User.php b/webseite/classes/User.php
index 0608b41..fecff9d 100644
--- a/webseite/classes/User.php
+++ b/webseite/classes/User.php
@@ -36,6 +36,10 @@ class User
      */
     public static function createUser(string $username, string $password): User|false
     {
+        if(self::getFromUsername($username) !== false) {
+            return false;
+        }
+
         if(strlen($username) > 100) {
             return false;
         }
@@ -141,6 +145,54 @@ class User
         }
         fclose($file);
 
+        unset($this->username);
+        unset($this->passwordHash);
+
+        return true;
+    }
+
+    /**
+     * Ändert das Passwort des Accounts
+     * @param string $oldPassword altes Passwort
+     * @param string $newPassword Neues Passwort
+     * @return bool true, wenn erfolgreich geändert, sonst false
+     */
+    public function changePassword(string $oldPassword, string $newPassword): bool
+    {
+        if(!$this->isPasswordCorrect($oldPassword)) {
+            return false;
+        }
+
+        if(!$this->logout()) {
+            return false;
+        }
+
+        $file = fopen(self::$userdataDirectory . self::$userdataFile, "c+");
+        if(!$file) {
+            return false;
+        }
+
+        $this->passwordHash = password_hash($newPassword, PASSWORD_ARGON2I);
+
+        $lastLine = ftell($file);
+        while (($data = fgetcsv($file, 300)) !== false) {
+            if (count($data) != 2) {
+
+            } else if ($data[0] !== $this->username) {
+
+            } else {
+                $data[1] = $this->passwordHash;
+
+                fseek($file, $lastLine);
+
+                fputcsv($file, $data);
+                break;
+            }
+
+            $lastLine = ftell($file);
+        }
+        fclose($file);
+
         return true;
     }
 
@@ -191,7 +243,6 @@ class User
 
         if(time() - $_SESSION["login_time"] > 86400 * 5) {
             session_unset();
-            session_destroy();
             return false;
         }
 
@@ -211,7 +262,6 @@ class User
         }
 
         session_unset();
-        session_destroy();
 
         return true;
     }
diff --git a/webseite/test.php b/webseite/test.php
deleted file mode 100644
index b3d9bbc..0000000
--- a/webseite/test.php
+++ /dev/null
@@ -1 +0,0 @@
-<?php
diff --git a/webseite/users/users.csv b/webseite/users/users.csv
new file mode 100644
index 0000000..761cc89
--- /dev/null
+++ b/webseite/users/users.csv
@@ -0,0 +1 @@
+admin,"$argon2i$v=19$m=65536,t=4,p=1$Wi9oVlZ2UjFFVUFTVDBYbg$fgYAK05urgS2+38wFPa9k1oO27O5B/J0CSWB7mUCYGU"