Join the Companions questline
Complete the Companions questline
Use the Witch Head from Glenmoril Coven during the quest “Blood’s Honor”
Return the Witch Head to the Flame of the Harbinger in Ysgramor’s Tomb
Defeat the werewolf spirit to cure lycanthropy
Repeat for any other infected Companions who need curing
Use the Cure Disease potion or Shrine of Talos before becoming a werewolf to prevent infection in the first place