If you are locked out of your server, you can try resetting your root password by going to Services -> Your VPS name -> Configuration -> Reset Password
Type and confirm your new root password and click Submit. Your VPS will reboot and this process may take few minutes until your password is successfully reset.
This process may not work if you have installed an OS directly from ISO. If that’s the case, you can always try the built-in rescue mode (Use Rescue Mode to troubleshoot your VPS) and manually reset your password.