Theres a little gap down the left of the power button(Viewed from behind the Vac) just enuff for a little tool, which you can buy on ebay, But I use a paper clip. Make sure its a fairly sturdy paperclip, and straighten it out. Put a small 90 deg bend in the end to leave about a 4mm leg sticking out. Then in the same direction, bend the top about 10mm out so you have an un-even U shape. This second bend helps you rotate the clip once you have it down the side of the switch housing. Put the 4mm leg down the small gap sidewards, and once about 15mm down, turn clip through 90 degrees. Your aim is that theres a little latch down there, which clips in when manufactured, your trying to push it back in, so you can lift the switch cover button up and out. Once you have done this, you can get to the screw which removes the whole switch housing box. It takes a bit of practice, and if you lever the housing over a little from the back you should see what your aiming for.
Hope this helps!
Craige, January 2007