Things You'll Need
Replacement trim rings (and baffles, as needed)
Recessed light fixtures come in a range of sizes, types and styles, but most fixtures have a canister (the cylindrical metal housing that holds the light socket) and a trim ring that covers the bottom edge of the canister and hides any gap between the canister and the ceiling hole. Some fixtures also have a baffle or deflector ring, typically a beveled or dome-shaped ring that surrounds the upper portion of the light bulb. You can buy replacement rings and baffles made specifically for your fixture model or product line, as well as universal rings made to fit specific canister sizes.
Turn off each light fixture at the wall switch and allow the light bulb cool completely. Remove the bulb from its socket.
Pull the trim ring down from the ceiling slightly and look for two wire springs or spring clips connected to the back side of the ring. If you have springs, unhook the spring ends from inside the canister, and remove the ring. If you have spring clips, pull the ring down from the ceiling as far as it will go, then squeeze together the two wires of each clip to release the clip from the canister, and remove the ring.
Measure the diameter of the canister and purchase replacement trim rings made for your size of canister. If your fixtures include baffles, you may be able to re-use the original baffles or buy replacements along with the trim rings.
Transfer the springs or clips from the old trim ring to the new ring, and install the new ring (and baffle, as applicable) in the same manner as the original.