Council members shall hold office for four years and until their successors are elected and qualified. Terms of council members must be arranged so that one-half of the council members in any city, as nearly as practicable, are elected in any one election. When a city first adopts the council form of government or changes the number of council members, or when a city that has adopted the commission system of government returns to the city council form of government as provided by section 40-04-08, the alternation of the terms of the council members must be perfected as follows: of the council members elected in each ward, the one receiving the greater number of votes shall serve until the first day of July following the second succeeding biennial    election and the one receiving the lesser number of votes shall serve until the first day of July following the biennial election succeeding the council member’s election; if the city is not divided into wards, the one-half of the council members elected in the entire city receiving the greater number of votes shall serve until the first day of July following the second succeeding biennial election and the one-half of the council members elected in the entire city receiving the lesser number of votes shall serve until the first day of July following the biennial election succeeding their election. Whenever, for any reason, vacancies exist on the council which require an unexpired term to be filled by election, the unexpired term must be designated on the ballot separate from any other regular term or terms that may also appear on the ballot. Candidates seeking nomination to an unexpired term are required to indicate whether or not they are seeking a regular term of office or an unexpired term of office on their nominating petitions as set forth in section 40-21-07.