Shut the electricity off at the main service panel. Identify the breaker that controls the lighting circuit and turn it to the "off" position.
Remove the shade from the original ceiling light fixture and remove the light bulbs to expose the screws holding the fixture to the ceiling. Untwist the wire connectors holding the black wires together and white wires together.
Pull the center cover plate off the center of the fluorescent fixture. Grasp the center cover in both hands and squeeze the cover to release it from the tabs holding it to the fixture. The cover plate encloses the wiring and the ballast of the florescent fixture.
Slide a stud finder over the ceiling to locate the ceiling joists to install the 8-foot fluorescent fixture. Mark the location of the joists then pull the wire from the electrical box you uncovered in Step 2 through the knockouts on the 8-foot fixture. Screw the fixture to the ceiling joist using wood screws.
Wire the fluorescent fixture to the house electrical circuit by connecting the black wire from the electrical box to the black wire from the florescent fixture using an orange wire connector. Repeat this connection for the white wire from the electrical box and the white wire from the florescent fixture. Twist another wire connector onto the green ground wire from the fixture and the bare copper ground wire from the electrical box, connecting them together.
Replace the center cover onto the florescent fixture and install the 8-foot fluorescent tubes. Turn the breaker on inside the service panel that supplies electricity to the fluorescent light circuit.