what year is your X?

I'm not sure about after facelift, but for prior, you go through the diffuser area (you yank that out by holding the silver part with both hands and pull down slightly, then out). Once that's off you can see the backside of the reflector. From the inside, use a hairdryer to melt the glue that is holding it on all 4 sides (the borders). After a few minutes it should pull off inward pretty easily. Make sure to get all the glue residue off the body of the vehicle before putting the new one on.

__________________
'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr