Section 2. Where the town elects a new board or officer to perform the duties of an existing board or officer, the office of such existing board or officer shall terminate upon the qualification of the new board or officer. Where official ballots are used, the establishment of a new board or office, or the fixing of the term of office of town officers where such term is optional, or the increase or reduction of the number of members of a board, shall be determined at a meeting held at least sixty days before the annual town election. In towns not using official ballots the matter may be determined by vote at the annual meeting. Such vote shall continue in effect until rescinded. If a town votes to increase the number of members of any board, such increase shall be made by adding one or more to each class, to hold office according to the tenure of the class to which they are severally chosen, as will within three years effect it, and such vote to increase shall remain in force until the increase under it is accomplished. If a town votes to diminish the number of members of any board, such diminution shall be made by choosing annually such number as will within three years effect it, and a vote to diminish shall remain in force until the diminution under it is accomplished. If a town votes to reduce a board of three members to a single officer, such vote shall take effect at the following annual town meeting, and upon election and qualification of such officer the term of said board shall terminate; provided, however, that in towns where official ballots are used, unless the vote thus passed is more than sixty days before the annual town election, it shall not take effect until the next annual town election.