If you will be managing a VPS or Dedicated Server you will need access to root or a user with the proper permissions to do all you need. You will have to update the server, do a security check, configure the control panel (if you are going to use one) and all the other software that will serve your site might need to be properly configured for optimal performance. If you just have FTP details (provided by whoever you got the service) I don't think you actually have a VPS or dedi.