don,t try and prise around the whole unit, i did and made a mess. the only part you need to remove is the push button.
this is held in place by a small catch, push a thin knife down the side near the small hole on the button. once the button is off you will see a screw. remove this and the unit will lift out.
steve.
steve thundercliffe. thundercliffe@ntlworld.com, June 2004