a) obtain a weapon - preferably silver, but not absolutely necessary
b) become proficient in the use of that weapon
c) find a real werewolf
d) on the night of a full Moon, wait outside the residence of the werewolf
e) allow the werewolf to injure you in a non-deadly manner, but using your weapon prevent the werewolf from killing you (which a real werewolf will certainly attempt to do)
f) at the next full Moon, you should turn into a werewolf
Note that this is based on the legends of werewolves that I have read - mostly Eastern European, but some French or other nationality of origin. In those legends, people become werewolves because they are injured by a werewolf who is trying to kill them, and despite being wounded they escape death either by cleverness or strength and bravery. There is no other method of becoming a werewolf in those legends that I have read.