If memory serves, remove the speed control knob, and located either above or below the knob shaft there should be a recessed slotted screw, that when turned CCW, will retract those brackets. (I believe Nutone recommended installers fill the screw hole with some sort of putty to prevent any liquids from the counter to enter the screw area. So if you see a small area with a white or white/yellow substance, that may be covering-up the slot in the screw). Good luck.