Steps to replace bathroom vent:

1. remove light and unit covers. 1 flat screw driver
2. unplug light unit, heater unit, and fan unit, unscrew screws to take these out.
3. undo screws that attach the metal box to wood frame and pull out box.
4. turn off electric and disconnect lines, mark each line with tape so you can still connect to the right circuits...
5. find the right size replacement and reverse the steps...