Disconnect electrical power from the vacuum cleaner and place the unit on a table or workbench that is at a comfortable height.
Use the screwdriver and remove the dust covers that are concealing the motor area. All vacuum cleaners are different in design, but generally the motor can be accessed by removing the top cover over the suction side of the vacuum cleaner. The screws are typically located on the underside of the unit.
Set the cover aside. On one end of the motor blower unit will be the suction blower. This will be an enclosed metal fan. The commutator and brushes should be located on the opposite end of the motor. Some units will have the commutator exposed, others may have a plastic cover concealing the motor brushes and commutator. If so, remove this cover to expose the area.
Use a small piece of emery cloth and gently polish the copper wedges or bars that make up the commutator. You should not have to remove the carbon brushes from the holders in order to perform the polishing. Each copper wedge or small bar conducts the electrical power to the windings through a small copper wire. Be careful not to scrape the wire when using the emery cloth.
Take a cotton ball and pour a small amount of alcohol on it. Use the wet ball to clean the surface of the copper commutator from debris and dust that remains after the polishing. Allow the alcohol to completely dry before reassembling the vacuum cleaner unit.