The same way you replace an indoor fixture.1) disconnect the power at the switch AND the breaker/fuse2) physically remove the fixture. They are generally held in with 2 screws to an 'octagon' electrical box. Each model is different. Just remove screws until you expose the wiring and the physical connection to the wall is gone3) undo the wiring. It should be black to black, white to white, and a green or copper ground wire to the metal box.Reverse the processa) READ THE INSTRUCTIONS ON THE NEW LIGHT.b) hook up the wire that holds the weight of the light to the ground screw (long steel/copper braided wire)c) attach the electical connections, ground, neutral (white), and hot (black) respectively, preferably in that order for safetyd) mount the light fixture to the box similar to how the old one was connected. Watch out for needing weather gaskets etc. (rtfm)e) install light bulbf) turn on breakerg) turn on switch, staying clear in case of asplosion.No asplosion = win.