Two: One to screw it in and one to observe how the light bulb itself symbolizes a single incandescent beacon of subjective reality in a netherworld of endless absurdity reaching out toward a maudlin cosmos of nothingness.
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.