Microsoft Confirms You Can Clean Install Windows 10 After Upgrading
 

This is one question that a lot of people have been asking, and Gabe Aul, the head of the Windows Insider program, finally answered it on Twitter today. Credit goes to Brad Sams at Neowin for catching this since it was a reply to another tweet.

Gabe states:

"Once you upgrade W10 w/ the free upgrade offer you will able to clean reinstall Windows 10 on same device any time"

http://www.anandtech.com/show/9334/m...fter-upgrading