Thanks for that, I hadn't found the "add a file" suggestion, despite extensive googling (probably asking the wrong question), but will bear it in mind.
I think the installation was beyond hope anyway.
The original problem I was trying to fix was that win 10 just wouldn't update - it wouldn't move on from build 1511 - the updates refused to install.
I wondered whether it was that there was not enough space on the hard drive (there should have been) and deleting the unwanted 100gb+ may have helped the situation.
The laptop is a fairly basic, 2011 model, is probably past it's "sell by date" and struggles a bit with win 10.
Tried to persuade the lady owner to move to mint but she didn't want to do that - can women be Luddites!!?
Thanks again