Unplug the Hoover-brand vacuum cleaner's power cord from the wall outlet. Press the button at the top of the cover so it can be removed from the vacuum cleaner. Twist the disposal bag off the nozzle at the inside top of the compartment. Dispose of the bag or save it for reuse later.
Upend the vacuum cleaner. Push the plastic lever at each side of the bottom away from the center with your fingers. Pull the bottom plate off -- some models will require removing screws from the plate with a Phillips screwdriver instead.
Locate the defective fan impeller; it is on one side of the motor housing inside the bottom. Grip the shaft that the fan impeller is on with the jaws of a pair of needle-nose pliers. Hold the shaft steady. Unscrew the fan impeller from the shaft. Dispose of the fan impeller in the trash.
Screw the replacement fan impeller on the shaft. Continue screwing the fan impeller on until resistance is felt. Remove the needle-nose pliers from inside the bottom of the vacuum cleaner.
Place the bottom panel back on. Push the two plastic levers back toward the center of the vacuum. Place the vacuum cleaner right-side-up. Place the bag or a new bag inside the front of the vacuum cleaner and reattach the cover.