Set a stepladder under the recessed fixture having its bulb changed. Completely extend the ladder's side brackets and snap them into place to ensure the highest level of safety. When using the ladder, never stand on the very top above the last step. Keep both feet on the ladder at all times and readjust the ladder if you have to lean too far to reach the fixture.
Extend your hand fully and place it with your palm up under the lens around the retaining ring.
Press firmly on the retaining ring and twist it counterclockwise. Some rings are threaded and some have a locking mechanism. In either case, twist the ring as much as it takes until it can be fully detached. The lens will drop down without the ring holding it, so be careful to support it so it won't fall and break. Place the ring and the lens in a safe place while you change the bulb.
Unscrew the old bulb counterclockwise and replace it with a new bulb of the same type and wattage. Screw the new bulb into the socket clockwise until it is snug. Don't over-tighten the bulb.
Place the lens against the bottom of the recessed fixture and twist the ring clockwise over it to secure it.