Do you mean the bullet clips that hold the light into the body of the car? If so, then you just need brute force, make sure you're pulling/pushing the light directly away from the car (ie straight back), not to the sides, otherwise they can bend and snap. Once you get them off the first time it makes subsequent efforts much easier (both from learning and from the clips coming out easier). Another option is maybe giving the studs inside the boot a bit of a love tap, but nothing too hard as you don't want to crack the plastic rear housing (if the clips bend/break then the studs and nuts are the only thing holding the light in)