Replace the entire headlight assembly and electronics. That's if you're looking for OEM parts. Otherwise, there are aftermarket options, but you're pretty much required to pulled the housings apart to install the projectors. Then it's a matter of having the HID ballasts and bulbs. Not impossible to do, but takes a little bit of skill and really big balls.
For what it's worth...I had Bi-Xenon projectors retrofitted on my '11 Wrangler in the stock housings. Cost me about $500 shipped to have a guy do them for me. Best mod I've done to my Jeep, too.