Depending on which side, open up either the Fuse box panel (on left hand side boot area) or the pump and gunk storage space (right hand side). Inside should be a cable running into the light fitting. Remove this the you will see two light grey knobs. Unscrew these but be careful not to drop them into the cavities as they are a bast**d to retrieve. Now, gently pull the whole light unit away from the car allowing the rubber seal (round plunger type thing) to pull through. The panel in the back of the light fitting will allow access to the bulbs.
The refit is the reverse, but arm yourself with a bit of cord or string. Pass through the light fitting where the rubber plunger is and loop t around. Offer the light fitting into place then pull the cord back through keeping hold of both ends. It should pull the rubber plunger back through. Then rescrew the grey knobs, and reconnect the cable.