I did that a lot of years ago and in my case it was relatively simple, although it was messy cleaning adhesive off the walls. If you can find a manufacturer's name, check out how it SHOULD have been installed and go from there.

The wall panels are designed to lap over top of the flange on the base. It shouldn't be a problem to remove them unless they glued the overlap, in which case it may be a little harder, but still doable.

Adhesive on the walls doesn't matter, because you'll want to demo any drywall that's behind the fiberglass walls, as you need to replace it with cement board to back the tile.