Most people replace the brushes and internal voltage regulator as a unit. It is very simple with two "straight" screws holding it in from the rear.
If you want to replace the brushes remove the regulator. The brushes are soldered to it. If I remember correctly the Bosch # for brushes is 11 011. After unsoldering the brush wire, feed the new wire from new brush (there are two) through the tentioning spring and resolder. Be aware that the wire determines the usefull length of the brush travel. Solder it short enough to hold the brush far enough into its socket that it stays in place (this is absolutely necessary for reinstallation back into the alternator. But not so short its usefull life will be shortened.
Bosch Master, ASE Master, L1
33 years MB technician