Two. One to change it and one to yell "Ta-daa!" when he's done.
Nun.
Just two, but you're going to need a lot of patience and light bulbs.
One, AND IT'S NOT FUNNY!
One. He just stands there with the lightbulb and the whole world revolves around him.
Dad: yea sure yells up to me son, you live with this guy now!
Three; one to drop the bulb and two to yell "pick it up pick it up!"
Phillip