How to remove large bushes?

There are two very large bushes in our yard and I want them gone. I may end up hiring someone to do this, but am wondering how difficult it would be to do myself.

If I cut them down with a chainsaw (?) how do I keep them from growing back? Do I need to kill the stump or what?

I want to put above ground flower beds where these were. (I can’t imagine digging there with all of those roots!)