Uninstalling Your Product Key
The first thing we need to do is get our activation ID, to do this fire up an administrative command prompt and run:
Windows will open a message box and tell you a bunch of information about the license status of your PC, take note of your activation ID.
To uninstall your product key you need to use the /upk switch, along with your activation ID:
slmrg /upk XXX where XXX is your activation ID
If you do it correctly you will be told that your product key has been uninstalled.
Installing Your Product Key
Installing your product key on your new PC is just as easy, all you need to do is fire up an administrative command prompt and use the /ipk switch.
slmgr /ipk XXX where XXX is the Product Key
NOTE: You need to type in the product key. Not the activation ID you got from the uninstall step.
If your key is valid you will be told that your key was installed.