Use the diagnostics key to upgrade, but please note, if you want to go back to Windows 10 Home, you will have to perform a clean install:
Upgrade to Windows 10 Pro using the following default product key:
VK7JG-NPHTM-C97JM-9MPGT-3V66T
Review instructions how to perform an Easy Upgrade using the default key:
How to Perform an Easy Upgrade in Windows 10
http://answers.microsoft.com/en-us/windows/wiki...