In reply to john arran:
My experience of upgrading an atom-based all-in-one, way back in late 2016, was that the install wasn't toooo bad. But the result was incredibly sluggish, taking lots of CPU doing nothing. I quickly gave up, and used the automated reversion to Win7, which took just 15 minutes.
At the time, I didn't have any active virus checking running, just Defender. Having recently installed Microsoft Security Essentials, I suspect that the sluggish performance was the Win10 implementation of MSE, which, as I understand it, is installed by default. So my comparison at the time was probably unfair.
I did a last (allegedly) update of my Windows 7 machines last night. Ironically, MSE running on one of them takes up so much resource (it's only got 1GB of RAM), that Windows update can't install the monthly security update, and MSE cannot install it's new security definitions. So the thing that's supposed to be protecting my security is actually damaging my security... May have to uninstall MSE (if I can get it to let me), so I can do the final WU.