pre-facelift is nice & simple i believe, carefully prise off the plastic cover infront of the foglight, undo 3 screws holding the foglight to the car & then undo the connection plug behind it. ( reverse for refitting after doing whatever your doing - the cover can be fiddly to get back on right as its a tight fit but goes in OK eventually :} )
it will be pretty similar for the facelift version too i suppose but there maybe the odd difference.
if you stand in front of the light unit, you will find a small hole in the underside of the bumper under the light. Undo the screw for about 3 full turns, then you will be able to remove the light unit out from the bumper.