Someone gave me their old pc for free, and it has 32 bit windows 7 on it. I'd like to install 64 bit windows 7, but need to know if the existing product key will work or if I will need to buy a new one.
Unknown. Where did this OS license originate?
If it was a preinstalled OS on that device, it may be 32bit only.
If it was from somewhere else, it is probably valid for a 64bit install, on that same hardware.