The roof snaps in place, you can pop it off using your finger nails, the undec ones come partially assembled, so won't be much help to show how to take them apart.
Thanks gents, appreciate the advice. This will be my attempt at painting rolling stock so I am a bit apprehensive as I don't want to destroy anything beyond repair. With all of this info, I am now eager to get the cars to work on.
The lettering does not come off easily, if at all. The MT cars, do however, strip easily in a bath of 90% ISO. You'll have a clean unpainted model to work with from there.
Looks as though I either leave them as is or strip them completely so looks as though I will be stripping them completely. Forgive me if this has been answered but how long should the shell be left in a bath of alcohol for the paint to strip?