It's relatively easy as far as instructions go... when you buy the new flares, make sure you buy the black plastic rivets (think at least 15-20). You need a plastic rivet tool (preferably angled)... the existing flares have rivets that need to be popped out via flat-head screwdriver. There are also pop-in white rivets near the middle for the 2 rears. Simply pull those outward to remove those.

Re-place with the new flares and pop in with brand new rivets (old ones not re-useable) with the plastic rivet tool. If you don't have a rivet tool, you will need 2 people and some extra strength + finesse as it is difficult to both keep the rivet in place and pop the stem outward (to lock it in place) on such a small rivet. I wouldn't try that again without a rivet tool... I haven't even finished all the rivets, procrastinating. Oh the 2 rears have the white rivets that are reuseable... just slide them into the new flares (you'll see what I mean looking at the old one) and pop them into the frame of the vehicle.

Takes about an hour.

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'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