- 1). Turn off the fish tank light and unplug the cord form the electrical outlet.
- 2). Place one hand on either side of the light ballast, which sits on top of the fish tank, and lift it off of the tank.
- 3). Turn the light upside down and place it on a flat work surface such a table or the floor.
- 4). Remove the existing light from the light fixture. If you have a standard incandescent light, compact fluorescent light, LED or metal halide, simply grasp the bulb in your hand and turn it counterclockwise to remove it. If you have a fluorescent tube light, grasp both ends of the light bulb tube with your hands and pull the bulb away from the fixture.
- 5). Discard the used bulb.
- 6). Insert a new bulb into the light ballast by reversing the steps taken to remove the old one.
- 7). Pick up the light fixture and turn it over so that the light bulb faces downward. Place the light fixture back on top of the aquarium.
- 8). Plug the light's electrical cord back into the wall and turn the light on.