Microsoft has confirmed that users who free-upgrade their Windows 8 or Windows 7 to Windows 10, will later on be able to format and clean-install Windows 10 on the same device.

Gabriel Aul, of the Windows Insider program, tweeted:

Once you upgrade W10 w/ the free upgrade offer you will able to clean reinstall Windows 10 on same device any time.
The key words are on the same device only!