Activate Windows 10 with W7/8/8.1 keys

 

The latest preview release of Windows 10 includes the first glimpse of a new feature designed to eliminate one specific activation headache. When this change rolls out to the general public next month, you'll be able to use your Windows 7, 8, or 8.1 product key to complete a Windows 10 upgrade.

see more in:

http://www.zdnet.com/article/next-big-windows-10-release-will-ease-activation-hassles/?tag=nl.e541&s_cid=e541&ttag=e541&ftag=TRE7ce1dc9