You are allowed to have two activated installations so you can retain the Windows installation if your prefer. You probably will after reading what follows. If you do not want to have the backup available then the minimum you need to do is deactivate it on the machine by opening one of the applications and choosing Help -> Deactivate.
Your CS5.5 license is only valid for a Windows system. It is too old to be swapped for a Mac license (only the latest version (CS6) can be). The only way to possibly get it on the Mac will be to install Windows emulation software on the Mac..