Two, one to screw it in, and another to say "Sock it to Me." (Notes: Sock it = Socket. Also, for the infant readers among you, this was a popular catch-phrase from "Laugh In.")
Four. One to change it, one to sing about how heartbroken he is at the loss of the old one, one to sing about how madly in love he is with the new one, and one to go "Yee-Hah!" and throw his cowboy hat in the air.