A school district which is not a cooperative school district as defined in N.H. Rev. Stat. § 195:1 may have a school board of 3, 5, 7, or 9 members, as it shall determine by vote at any annual meeting. They shall serve for a term of 3 years. Insofar as possible, an equal number of the members shall be elected at each school district election. Whenever such a district determines to change the number of board members, it shall also determine the number of members to be elected each year. Such change shall not take effect until the school district election in the year next following the one in which the change is voted. The board will increase or decrease in membership so that there will always be an uneven number of members until the desired number is reached. The school board of a district which does not otherwise vote shall have 3 members.