Yes, it is. I recently did update a system for a friend and it worked fine.

I just entered the win7 registry code on the m$ Website and got an iso, which asked for the key once again during installation.

Afterwards i had a fully legal win10 system.

It was a OEM Win 7 and you cannot use the m$ iso downloader, as it claims you should contact your hardware vendor. You need to use the update program site. Just google for it.

[ Edited by geit 31.01.2017 - 09:50 ]