Upon certification of a resolution declaring the need for a commission to operate in a city or town, the mayor and governing board thereof, respectively, shall appoint, as members of the commission, not less than five nor more than nine citizens who shall be residents of the city or town in which the commission is to operate. The governing body may at any time by resolution or ordinance increase or decrease the membership of a commission, within the limitations herein prescribed. (1951, c. 1095, s. 5; 1971, c. 362, ss. 6, 7; 1973, c. 426, s. 75.)