I did this yesterday mate.. You take the grill off, it just unclips, theres two bolts on the top of the lamp and two at the bottom, then its off.
Nest you pop the little clips off and i used a hair dryer to seperate the lenses, you heat up the edges of the glass where the silicone is, for a minute or so then gentley prize them apart with a screwdriver. Give then lenses a good clean then put it back on and reheat with hairdryer tomake sure the silcone is re-sealed nicley!
Jobs done..
Rich