Many thanks, Sea Vixen.
Will do. Reading the tutorial and, for anyone else's benefit, I only had a Win 7 Pro upgrade disc so I couldn't do a complete reformat pre the install as, I understand from other posts on this forum, that the upgrade application needs to read the key of the existing installation before you can use it successfully.
I did, however, the next best thing, and deleted all partitions and a format from that point, hence I have the Windows_old file.
I can now do as you say and take out the data files that I need - though I had backed these up - and delete the whole Windows_old file, giving me a lot more space.
By the way I love the real Sea Vixen. I fly two seat puddle jumpers myself and not sure how I would cope at twice the approach speed onto a runway that was moving 60 feet up, or down, and probably wasn't where I last left it, in any case! Profound respect to those that could.