On our (former) Autoquest 100 the dome covers clipped into the bevel. The way to remove the cover is to slide a slim blade between the cover and bevel and gently lever the clips out.
The bevel is part of the main fitting which is screwed to the ceiling.
Replacing the fluorescent lamp with LED (which I did in ours) is simply a matter of cutting the wires to take the ballast & lamp socket out of the circuit and wiring in the LED with a block connector. Remember to cut the wire from the switch on the correct side of the switch
The dome cover simply clips back in after the job is done.
Graham