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.
Since your company sells managed VPS solutions, I'm curious why this specific question? Is this simply for educational purposes? If you have FTP details, then which do you have these details for? A VPS or a dedicated server?
█ ProlimeHost- Dedicated Server Hosting & KVM SSD VPS
█ Three Datacenter Locations: Los Angeles, Denver & Singapore
█ SuperMicro Hardware | Multiple Bandwidth Providers | 24/7 On Site Engineers