How or where do you replace the tires if bought online?

ShockWave

take it to somewhere that cares about ur rims. Get a shop manager to walk around the car first and check the rims before they touched it. Ask them to get the best guy on the job. Bring a camera and take lots of pictures of the wheels they gonna be working on right in front of them so this way they know you have pictures just in case. When they are done make sure u check the rims very good. Clean all the dirt off and check inside and outside. Check around the wheel weight balance also. If you see any marks tell the manager right away! Don't leave the shop! If they mess up ur rims rise hell and tell them you want a NEW SET!!!