Replacing a wall light is one of the easier do-it-yourself projects as long as you remember two things: never work on any electrical system without cutting power at the house fuse box; and make sure the base of your new fixture is slightly bigger than the base of the existing fixture. Even if the wall is painted under the current fixture, that paint will likely have aged differently than the exposed paint on the wall, meaning you'll have to repaint if you don't completely cover the space.
Turn off the electricity to the light fixture at the fuse box.
Remove the screws holding the fixture to the wall and pull it out enough to reach the wire connections behind it. Disconnect the wires and pull the fixture completely free. Leave the wires hanging from the exposed electrical wall box.
Take off the mounting bracket from the old fixture, which will be attached to the electrical box with screws.
Locate the mounting bracket for your new fixture (it will be a flat plate or strip of metal). Set the bracket against the electrical box, line up the screw holes and affix the bracket to the box with the provided screws. Pull the wiring out around the bracket so the wire ends are still accessible.
Hook the copper ground wire from the electrical box around the green ground screw on the bracket. Tighten the screw.
Hold the new fixture near the box. Connect the black wire from the fixture to the black wire from the box by holding the wires next to each other and twisting a wire cap over both of them at once. Do the same with the two white wires.
Hold the fixture against the bracket and line up the screw holes on the fixture with the screw holes on the bracket. Secure the fixture to the bracket with provided screws. Turn on the power.