It can simply be (carefully) levered out using a small, flat bladed screwdriver. On the back will be a multiplug, unplug this but have a bit of insulation tape or similar ready so you can stick the cable to the trim outside the hole you've just left - you don't want the cable dropping in there and you having to start unscrewing trim panels to retrieve it. As I said, take the switch away from the car and douse the living bejesus out of it with WD40 then just leave it to dry. Once dry, refit and see if it works. There's no guarantee, it might well be knackered after all, but it's worth a go for a few pence worth of WD40. It worked a treat on my driver's side window switch 2 years ago and that's been fine ever since.