What is the best way to "fire" my advisor?
If you are having trouble with your advisor, I think you should talk to your department's director of graduate studies (or the equivalent). At most universities (at least all the ones I have been at), there is someone whose job it is to handle paperwork and the such. They are also there to act as a kind of ombudsman, helping students handle disagreements with advisors.

I've had this role before, and I view myself as squarely on the side of the student. I can fight advisors on their behalf. I've done all of the things you are asking for: navigating committee changes, telling an advisor they are no longer a students' advisor, etc.

I think it is important to document such behavior on the part of the advisor. Even if your breakup with the advisor goes poorly, an official record of such behavior might make the department think twice about allowing such a pattern to continue.