Like many companies and organizations, the Postal Service has a board that oversees operations. This board is called the Board of Governors. One of its roles is to select the Postmaster General.
The Board of Governors itself is made up of as many as nine governors, who are appointed by the President and confirmed by the Senate. No more than five governors at any one time may be from the same political party. The governors select and have the authority to remove the Postmaster General. The Postmaster General is a member of the Board, and participates in the selection of the Deputy Postmaster General by the full Board.