It's quite tricky! If you look at the button from above, there's a flat side with a small rectangular hole just to the side of the button. If you can get something in there like a tiny screwdriver you should be able to push the 'snap-fixing' of the button away so the button slides off. How you're supposed to do it without breaking the button's 'snap-fixing' is beyond me as it's very stiff and awkward to get to. Mine broke and now although it works the button can be pulled off!. Once you've got the button off there's a screw behind it to get to the guts of the switch.
Hope this is enough info.
Joe, December 2008
