Disconnect the terminals of the battery. Use a spanner to loosen the bolts present on top of the alternator. Some alternators may also have the same bolt present underneath them.
Move the alternator in the direction of the motor so you can take of the belt from the pulley. Disconnect both wires connected to the back of the alternator and remember to label them to avoid confusion later on. Take out the alternator out of the socket.
Locate the voltage regulator on the back of the alternator and remove it; it will be a small button like thing on the back side of the alternator.
Open the voltage regulator carefully and remove both worn out brushes. You should remove the brushes one at a time through the space present in the regulator. Attach the new brushes after cleaning the inside of the regulator.
Attach the regulator back in its place and fix the alternator back in its slot. Connect the wires in the same sequence and oil the bolts. Insert the bottom bolt first and align the alternator with the top bracket. After correcting the alignment, tighten the top bolt and reattach the belt with the pulley. Congratulations on overhauling your alternator.