Changing bathroom spotlights, the front over of the light is not twisting off, what can I do?

It could well be that the casing has warped/buckled due to the heat. This is a common problem with the cheaper recessed spotlights and often they have to be broken to get them out.

If you can pull the fitting out the ceiling and safely disconnect it from the circuit, then try using some WD40. Mind your fingers on the springs as they snap out. Should this fail then a little heat might do the trick. A good pair of gloves such a thick gardening gloves will help. Another little trick is to try to tighten it too before trying to untighten it. Hope this helps.