The salary of the Mayor shall be fixed and determined by the Council, but the salary of the Mayor shall not be increased or decreased during the term of office which such person is serving. If the established salary of the Mayor is to be changed in respect to a succeeding term of office, such change must be made by Council prior to the first day of July of the last year of the term being served by the Mayor. Unless or until such salary is so changed, it shall remain as last fixed.