Remove the lens cover from the existing light fixture by unscrewing the screws.
Remove the old bulb by twisting it out of the socket. Place the new bulb in the socket.
Replace the lens and screws back into the fixture.
Turn off any electrical power to the camper trailer. Remove the lens cover with a screwdriver. Unscrew the light bulb. Depending on the fixture, you may need to unscrew or unbolt it.
Disconnect the wires running to the fixture.
Connect the wires to the new fixtures, matching polarity.
Fasten the new fixture into place with screws or bolts. Install the LED bulb, and replace the lens.