You need a pair of "U" shaped wire radio extractors. Most car spares places will do these for a couple of quid. Get the right ones though as the sizes do differ for different car manufacturers. Insert into the holes on outer front edges of the radio and gently push the extractors apart. This releases the holding clips so now just withdraw the unit (keeping the pressure on the extractors while you do it).
VL1500 TONY, October 2009