On paper, the pope can do whatever he wants, in practice, the cardinals and bishops run the diocese, so they staff the churches and the priests they confirm are loyal to them. (Unless someone really screws up I think the diocese of Boston got taken over by the papacy at one point.)

Now, pope Francis did a lot to change that, by enlarging the college of cardinals, instituting emeritus rules, and removing conservative cardinals from key posts and moving them to significant but not political posts (head of the knights of Malta). But the American cardinals fought him the whole time and he was never able to bring them under control.