license - How to remove or deactivate my windows 7 licence on one computer and use it on another

I want to remove my windows 7 genuine licence from one computer and install windows 7 on another computer using the same licence key. I know the licence is somehow locked to the hardware of the original computer - but is there a way to uninstall the windows licence, so it can be re-used, and locked to new hardware?

(The original PC will go back to XP)