How to remove wasp nest and let them leave
As Ed B. commented,  by knocking down the nest, you'll convince the wasps to leave and build a new nest elsewhere.  It's not necessary to spray -- at least from the point of view of getting them to leave! -- as they'll abandon a fallen nest.  The difficulty comes in whacking the nest without getting a swarm attacking you.  If you're fast :-) you can wait for a very cool night, hit the nest with a long pole, and run inside.

Otherwise, some spray to at least kill the exterior wasps and dissuade insiders from coming out a poisoned entrance should precede the knocking-down step.