The one in question? This guy. He and his buddies were exterior lights around our house.
Begin by turning off the circuit breaker to the particular room or section of the house by which you're working. You don't want to electrocute yourself. Then, remove the light fixture from the wall or ceiling.
When you remove the light figure, be sure to remove the copper ground wire from its grounding screw. The new light fixture will have its own ground wire.
That T-shaped piece is called a crossbar. Remove the crossbar from the outlet box.
Those plastic yellow caps are called wire nuts. They twist onto the end of each wire to fuse them together. Take off the wire nuts to expose the copper wiring within. (Most new fixtures come with enough wire nuts for each wire, but it's usually a good idea to hold on to the old ones.) After doing so, pull the old fixture's wires off of the house's wires.
With the wire nuts removed, you will have three exposed wires. The copper one is the ground wire (sometimes it can be green). The black wire is positive, and the white wire is negative. Your new light fixture will have its own set of ground, positive, and negative wires.
For the next step, cut yourself a couple strips of electrical tape and stick them in a place that's easily accessible.
Generally, match the colored wires from the wall to the colored wires from the fixture. When in doubt, refer to the instructions included with the new fixture. Bond the house's and new fixture's wires together by twisting on the wire nut. Cover the base of each wire nut with electrical tape to ensure that they'll stay put.
Stuff the three wires back into the outlet box and affix the new fixture's crossbar. Attach the ground wires to the ground screw of the crossbar once done.
Then, hold up the light fixture against the wall or ceiling.
Light fixtures are usually mounted by screws of some kind. Tighten those, as necessary.
Once done, turn on the circuit breaker and test your new light fixture! Depending on the fixture, it usually takes Evan about 15-20 minutes to install it. Ceiling fans and chandeliers tend to be more complicated just because they're heavy, awkward, and have more decorative parts to them.
Remember the old?
Well, here's the new!
What a difference a pretty light fixture makes, right?