HDD is 19 Gb and the free space is 10.9 Gb - that's after the recent exercise.
I followed markjoy's instructions as best I could but there was nothing which was an absolutely exact translation of what he told me to look for, because I have Spanish Windows. Certainly what I ended up with appears to have been more comprehensive than expected, as I tried to explain higher up, and appears to have worked. I have since done some exploring in it's set-up criteria and believe that I have left it with instructions to repeat the exercise once a month with each step being separated by a day or two so that there is a chance for all to be completed in turn should I have the machine turned off at the exact time appointed for each.
Thank you all once again for your attention and advice. I hope to be able to repay by helping someone else with something within my areas of expertise some time in the future.