Wynne,
I have a different make of van and microwave but would guess that they are all fitted similarly. Mine packed in early last year after only a few weeks use and was replaced under warranty. By my own choice rather than take my van to the dealer to have the microwave replaced I just removed it from the van and picked up the new one and refitted it myself.
If you look under the cabinet which houses the microwave you may find a couple of screw heads, undo these and the microwave will lift out. On mine, a flat piece of wood had been screwed to the base of the microwave and this is what the screws under the cabinet were fixed to.
As to the possible reason for the micrwave packing in - There is a known problem with certain makes of van having insufficient ventilation around the microwave causing to overheat and either cut out on a temporary basis or pack in altogether.
Bailey have now introduced a modification for their Senators to try and eliminate this.
Robert