Then I think your only alternative is to boot a WinPE USB or CD/DVD and rename the file while it is not in use by the system.
Thank you Miles.
I don't understand WinPE, so haven't got that facility.
What I do have is Microsoft's disks (32 and 64) which I bought from Microsoft. The computer was bought new from HP with Windows 8.1 pre-installed. However it had a lot of "extras", including games and HP stuff. With the newly acquired (64) disc from Microsoft I reinstalled from scratch in the original partition - so losing all the extra rubbish.
Some time later I encountered a problem with the PC not booting up. I searched Google from another machine (with XP) for a solution but couldn't find anything - it just wouldn't boot.
I took it to a local IT company who overcame the problem. I have no idea what that involved.
I recently discovered that Windows Update was not working. I also found that I can't refresh the machine. Someone is trying to help with this and I don't want to step on any toes by asking here or anywhere else. I started this thread just to ask for assistance in overcoming the inability to be granted full (hidden) administrator privileges which is needed in order to perform the actions required by the other helper. I tried following Fred Langa's procedure, which appeared in Windows Secrets, without success.
It looks to me as though the easiest route in the long run would be a refresh, a repair, or complete re-installation - except that refresh doesn't work. The system gets so far and coughs up a message saying that it can't complete or whatever. It then proceeds to undo any changes so I'm back where I started.
Is there a sure-fire way I can reinstall the operating system?