This one is actually covered on eHow.com. Let me give you the highlights:
1. Lift and properly support the hood on the Impala. Locate the carís battery and then use a socket wrench to remove the black ď-Ē cable from its post on the battery.
2. Wrap the metal terminal at the end of the cable completely with electrical tape. There should not be any metal showing after wrapping the terminal.
3. Position the battery cable away from its post on the battery as well as any other metal it may accidentally come into contact with.
4. Wipe the wiring harness plugs connected to both of the radiator fans with a clean . . . rag. Then unplug each of the wiring harnesses from their individual fan and remove the wires from the retaining clips. If the safety clip on the wiring harness plugs seem hard to lift by hand, use a flat-head screwdriver to lift the clip upward while removing the plug.
5. Apply the . . . emergency brake and then raise the front end of the car. Place a jack stand on the left and right frame rail behind both front tires.
6. Slide under the front end of the car so youíre able to see the radiator. At the bottom of the fan unit, you should see two plastic push-pins. Remove the two push-pins with a flat-head screwdriver and then stand back up in front of the car.
7. Remove the two top bolts with a socket wrench on the left and right side of the radiator fan unit. Then carefully lift the entire fan unit vertically out of the engine compartment.
8. Install the new radiator fan unit by reversing the removal steps. Tighten the two top radiator bolts with a 1/4-inch-drive torque wrench set to 53 inch-lbs. and then tighten your battery cable with a 3/8-inch-drive torque wrench set to 12 ft-lbs. until secure.