Windows 7: Unable to rename top-level Administrator user name

I am a new Windows 7 user running Home Premium on a basic laptop that was originally my wife's. When she gave it to me it was running XP. As I am a died-in-the-wool Mac user, but also need to run Windows apps (e.g. MS Publisher), I upgraded the OS to Windows 7, being the closest GUI to a Mac. My biggest beef is that as the original Admin my wife's user name appears as the machine's owner and I want to change that. I have read several threads here, and followed advice but am getting nowhere, as her user folder is locked so I cannot rename it. I cannot delete it (or at least do not want to risk it) as that is where the Windows 7 OS resides. All help gratefully received.