The board of trustees of every savings bank may, by resolution incorporated in its bylaws, increase or reduce the number of trustees named in the original charter or certificate of authorization.

(1) The number may be increased to a number designated in the resolution not exceeding thirty: PROVIDED, That reasons therefor are shown to the satisfaction of the director and his or her written consent thereto is first obtained.

(2) The number may be reduced to a number designated in the resolution but not less than nine. The reduction shall be effected by omissions to fill vacancies occurring in the board.