Upgrade to premium: domain type question

Hello,
My account was suspended for violating 20%+ CPU usage limit and I am going to upgrade it to premium in order to reactivate it.
I want to continue to use the same domain name (tammiku.site40.net). Which option should I select during the premium service registration: “Use an Existing Domain” or “Transfer the domain from another Registrar”?
And do I have to copy all the files and sql-databases to the new server after upgrade?