> Run command prompt as an Administrator.
> Enter slmgr /upk and wait for this to complete. This will uninstall the current product key from
Windows and put it into an unlicensed state.
> Enterslmgr /cpky and wait forthis to complete. This will remove the product key
from the registry if it's still there.
> Enterslmgr /rearm and waitfor this to complete. This is to reset the Windows activation timers so the new users will be prompted to activate Windows when they put in the key. This should put the system back to a pre-key state.
Hope this helps you out!