Isn't he, like, the boss of them though? If you're the Pope and you don't like a particular bishop then you reassign him to a diocese in the middle of the Sahara or wherever and put your own guy in his place.
Heck, this even works with cardinals - maybe you can't traditionally un-cardinal a cardinal, but you're an absolute monarch and you can make up whatever new laws you like - if you want to make it look more official then you assemble a council of a dozen other cardinals you like and get them to do it, but either way, if you want to get rid of the guy there's nobody really stopping you.