Go buy a couple cans of AIRCRAFT REMOVER from Walmart. Spray it on and let it sit. It will bubble the clear coat off.......looks really crappy during the process. Also, if you are doing this with tires on, tape off the tire by the bead and protect it from that stuff. It will bubble rubber on the sidewall.
After it sits (apply generously and recoat as needed), get a good pressure washer with a turbo tip preferably. Regular tip will work to, just not as fast. Once you have bubbled up looking mess, pressure wash them and watch the crud now off!!
After that, you should see bright aluminum material. You may have to reapply if you have stubborn areas. Once cleaned up you can polish as needed or paint whatever color you like. Be sure to add a couple coats of clearcoat when done to seal it all up.
I've done multiple sets of wheels this way and have had good luck