Shut off the power to the light circuit at the main electrical box.
Use a drill/driver to remove the mounting screws holding the fixture in place, then remove the fixture (Image 1).
Unscrew the wire nuts on the ends of the exposed wires and use a circuit tester to be sure the power is off. Detach the wires from the fixture.
The wires extending from the junction box in the wall may be “pigtailed,” or attached to other wires. If so, leave these wires connected — exterior lights are often wired together in a series so all can be turned on with one switch. The wires of the new fixture (Image 2) will be attached to these interior wires in the same way as the old model.