Several months ago, I cloned my Windows 7 installation to another hard drive and then upgraded that installation using the free Windows 10 upgrade offer. That went fine.
The one-year anniversary update, however, was a monumental and epic failure.
Pressing the reset switch on my computer and rebooting three or four times after the failed upgrade finally managed to get Windows to roll back to its previous installation version. I then went back to using the Windows 7 hard drive on that computer.
This is exactly why I use and recommend Linux.