Any proposal to change the form of government shall be initiated by a petition signed by at least the number of qualified voters, equal to four for every 100 inhabitants of the city or fraction thereof according to the last federal census, and then filed with the city clerk. The city commission shall forthwith order an election, at which the legally qualified voters of the city shall vote for or against the proposed change in form of government. The officers and members of the governing body of such newly adopted form of municipal government shall be elected as soon as practicable under the provisions of law applicable thereto; and upon their election and qualification for office the term of office of all members of the commission and mayor under the mayor/commission/city manager form of government shall terminate.