Windows 10 Udate Activation Key
Refer: http://www.tenforums.com/tutorials/35979-product-key-uninstall-deactivate-windows-10-a.html
Remove the old activation key
C:> slmgr /upk
Clear the registory
C:> slmgr /cpky
Enter the new key - you may need to do through GUI today
C:> slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
Activate the key
C:> slmgr /ato