So I go to the Control Panel/Programs and Features, click on RailSim and select uninstall at which point I received a notice telling me that this operation would take approximately 1 hour
I have no idea what the uninstaller does, and to be fair it only took about 50 minutes, (and it did not delete the extra locomotives I had downloaded from the KRS site, but it did delete re-skinned textures I had made).
The re-install of my own copy went well and worked 'right out of the box', but I thought I would print my experience of this as I know a lot of users tend to reinstall programs every time they have a small error, this normally does nothing, but I suppose it makes them feel better.