Cheri from Ohio writes:
I have Win XP pro and I want to upgrade to Win 7 pro do I need to have the product key for Win 7 pro to upgrade my PC?
Sheri, according to Microsoft’s support forums, there is no direct upgrade path from Windows XP to Windows 7. It’s really a clean install which means, you must back up your personal files and settings using the Windows 7 Easy Transfer Utility. Microsoft offers a pretty detailed walk-through of the process at this link. 
The “upgrade version” of Window 7 was priced at a discount for those who already had a qualifying Windows system installed and activated. You will need the product key for the Windows 7 Pro in order to install it your PC.
You may also want to read this article about the Windows 7 Upgrade Advisor. 
Good luck with the switch!