Light fixtures come in all shapes and sizes, and most are fairly simple. Two to four surprisingly small screws attached to a square or round metal box called a junction box typically support the fixture. Before removing the fixture, it's important to fully support the fixture's weight once it is loose from its hardware. If it seems heavy, get help.
Turn on the light you intend to remove. Go to the breaker or fuse box and look for a switch labeled with the name of the room your fixture is in. Turn it off. Go back to the fixture. If it is now off, the power is disconnected. If not, look again for the proper breaker or fuse. Continue trying circuits until the power to the light is off.
Set up a stepladder under the fixture. Even if you can reach it from a chair, or other makeshift step, it isn't safe. Set up a second ladder if you need help to hold the fixture while removing it.
Remove the ceiling bevel on a hanging fixture. The ceiling bevel is the decorative plate against the ceiling that the wires run into. It is typically held in place with standard screws or small round, ridged bolt heads. Use a screwdriver or pliers to loosen the fasteners. Turn the screws or bolts counterclockwise to loosen them, allowing the bevel to drop down onto the rod or chain connecting the fixture to the junction box.
Remove the glass globe or other diffuser from the bottom of a fixture mounted tight against the ceiling. Look for a decorative nut in the center of the globe underneath, or screws above running horizontally into a metallic ring. Use a screwdriver or pliers to release the fasteners by twisting counterclockwise. Remove the globe and take the bulbs from the fixture to reveal the mounting screws in the fixture's base plate. Loosen these and turn the base plate counterclockwise to slip it over the screw heads. It will now drop down to reveal the junction box.
Disconnect the wires coming up from the fixture, one at a time. These are usually white, black and green. Cap off the wire coming down from the ceiling with a wire nut. The green wire is the ground and has no corresponding wire coming into the fixture; simply unscrew the fastener at the end of it to release it.
Support the fixture's weight at this point until it can be taken down. Remove the screws running through the metal mounting bracket attached to the bottom of the junction box. Two to four screws usually run up through a silver rectangular bracket. Once this bracket is removed, the fixture should be free. Lower it carefully.
Tuck the ceiling wires into the junction box and cover it with a flat junction box plate cover, using the screws that were supporting the fixture mounting bracket.