Thankyou gregrocker. I have now done what I wanted to do with this. It was not as straightforward as a simple deletion of two operating systems, as all three had been installed with one motherboard /CPU whereas I now have upgraded to a new set.
Originally none would boot. I did a startup repair using a WE7 installation disk, which resulted in the three systems being shown as "recovered".
Neither Vista nor W7 would boot but W8 opened as if it was being installed, and after a few screens for a few steps , this activity ended and the startup completed normally. The only thing then required was to get it revalidated as genuine.
I later used Mini Tool Partition Wizard to delete Vista and W7. To reload the boot files in W8 I used a PE rescue disk made using Macrium Reflect - it has a separate option to do this.
I now have W8 on a single partition.