is it a 2 button fob ?? if so read on
hold the fob with the 2 buttons on top and the blade pointing away from you
look at the rear end where you can attach a keyring, on the right as you look there is a slight opening between the top half of the fob and the bottom half use a very small flat bladed screwdriver and gently prise apart(very gently) the fob will then part
just out of interest does the battery appear flat?? if so before fitting a new battery when the fob is open try pressing the buttons inside the fob I have found that the rubber push button on the fob can wear out and a new battery has not been required I put a tiny washer to inside the rubber push
button to pack out the rubber button so far i have had no problems with it
I hope this helps let me know!!
Dave the Rave, April 2008