A: Only one but it may take him/her more than five years to do it.
Only one. Just as long as you hand him the damn lightbulb.
Two. One to change it and one to yell "Ta-daa!" when he's done.
Cessna: "To get my Commercial Pilots Licence and Instrument Rating." ATC: "I meant in the next five minutes not years."
We haven't spoken for five years".
A: Three - one to change it, one to not-change it and one to both change-and not-change it.
A lot, apparently. Have you seen their new building?
One to change the lightbulb and one to drive down to Kent to pick him/her up.
Ask him/her to pronounce unionized
Only one, but it takes nine years.