If you look at the underneath of the brake lever, near the switch, there's a hole. The switch housing has a small plastic tab that flares out and locks into that hole, so you can just use a screw driver to push on the tab through the hole and pull the switch out.
Disassembling the switch itself is easy too. Just shift the small metal band down, fold the rubber sheath back on itself and using numerous jewellers/precision screwdrivers, flare out the clips on the 4 sides. Once the outer plastic cover is off, the shaft will come out and the two contacts on either side can just be pulled out to the side. Reverse for reassembly.