Paul,
You will have to pull all the piping out of the front wall of the cab, and break the engineer's, and fireman's seats out. They are plastic, and glued in place, they come out easily enough with a little pressure from a small flatblade screwdriver.
Then, on the engine side, just in front of the step, there's a small plastic "wedge", held in place with a tiny flathead phillips screw. Remove the screw, and carefully remove the wedge, and the cab slides to the fireman's side and the three lugs will clear the frame and the cab comes up off the frame.
Pete