I'm very grateful to
Bree,
S1W2, and
Marie SWE for all this excellent advice about the different possible paths to W7 64-bit, and I'm currently looking at those ideas, links and downloads. I had no idea the "how to" of it could be so involved. So before I decide on the exact details of how I'm going to make the switch to 64-bit, it seems logical to first decide which OS (W10 or W7) would be the wisest one to go for. That way, if worst comes to worst and W10 "wins," I can just follow the TenForums tutorial which seems to be pretty simple and bulletproof, and if I end up opting for W7 then I can ignore that and choose my path from the suggestions in this here thread.
. . .I very much want it to be W7 so I can avoid all the W10 spyware and stick with the OS that I'm familiar with, but so many people out there seem to take it as read that sticking with the now obselete W7 would be a wrong move. Here are the only reasons I can see (so far) for their attitude:
1. W7 would be more vulnerable to malware and viruses,
2. New software and updates to existing software wouldn't work in W7,
3. It would mean missing out on useful new features in W10,
4. There are fixes for anything nasty (such as spyware) in W10, and
5. 64-bit W10 is free for legal W7 users while 64-bit W7 might cost a few pounds.
So here's my thinking so far on those points.
Vulnerability to malware and viruses (security):
How much more secure than W7 would W10 be? Is security an OS thing or a browser thing? If it's a browser thing, my Firefox updates seem more interested in whether my OS is 64- or 32-bit than whether it's 7 or 10, so I'm hoping that with 64 bits they'll update me just like they would if I had 10. I've used nothing but Firefox for browsing, with the plugins NoScript and CleanLinks. I know almost nothing about security problems that don't arise from browsing the Web, and have pretty much ignored that angle. Have I been skating on thin ice without knowing it?
New software and software updates:
Again, I'm hoping the use of 64-bit Windows will be enough. So far the only new programs and updates that have refused to work for me have done so on the grounds of their not supporting 32-bit any more. But then I've not installed many new programs or updates, so I don't know if my experiences are very representative. What do you think?
Fixes for nasty content in Win 10:
I gather a lot can be done to beat 10 into submission, but I've also heard rumours that the spyware can't be completely killed. I gather Cortana can be disabled but only at the expense of losing the search box in the Windows start menu, and that doing any kind of search with 10, even for a local file, gives a Bing search.
OMG! Looks like simply killing Cortana wouldn't be nearly enough then, and I can well understand your "Never 10" attitude. So, if a user did everything they reasonably could to thwart the spyware content in 10, what working spyware would they still have to accept? And if the user really went to town on this and killed all the spyware it was humanly possible to kill, would that be enough, and what useful features would also perish in the cleansing? Anything lost that didn't have a good (free or cheap) 3rd-party substitute?
. . .Has anybody written a unified, simple-to-use utility that makes the whole battle possible without investing weeks of time and tears into the process? It strikes me that without such a utility, or at least a single, comprehensive tutorial on how to do it all manually, the biggest problem is the fragmented nature of the subject - a user could spend a long time doing their best to fix everything they could, and they still wouldn't know they hadn't missed something. So, if your time was limited and you wanted the most complete one-stop shop to show you how to do the whole job, where would you go?
Cost:
It looks like 64-bit Win10 activation would be free for me as a legal 7 user, as long as MS don't pull the offer. There's a good chance that 64-bit 7 would be free too (
S1W2's activation backup and restore looks very easy and promising, thanks for that

- and if it doesn't work, you never know, HP might respond well to a phone call). I gather the unactivated version of 10 runs almost as well as the activated version. What does 7 do if it's not activated?