THANKS TO EVERYONE WHO REPLIED TO MY PLEA, and thanks for your patience with a novice.
I found various tutorials online relating to the use of curves, although most of these were related to color photography and I found it difficult to associate that with my grayscale image. However, I have now managed to improve all the drawings which were a problem I found it quite easy to neutralise the background, but more difficult to keep the thin lines of the drawing clearly visible.
I don't know if anyone can offer any comments on this:
I noticed something which has been evident previously when I was using the brightness/contrast adjustment. Using the preview I made adjustments until the image looked how I wanted it. After I OK'd the settings, the image changed (usually going lighter). If anyone can offer any suggestion why this should happen, I would be most grateful (again!)