1. In any district including all of a city of fifteen thousand or more population and in any district in which the voters, or the board as provided in section 275.23A, subsection 2 , have authorized seven directors, the board shall consist of seven members; in all other districts the board shall consist of five members. 2. A change from five to seven directors shall be effected in a district at the first regular election after authorization by the voters or the board, or after a district first includes all of a city of fifteen thousand or more population, in the manner described in section 275.37 . [C51, §1112; R60, §2031, 2035, 2075; C73, §1720, 1721, 1808; C97, §2752, 2754; S13, §2752, 2754; C24, §4198, 4212; C27, §4198, 4211-b3, -b5; C31, 35, §4216-c23; C39, § 4216.23; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §277.23 ] 2002 Acts, ch 1024, §2, 3 ; 2002 Acts, ch 1134, §89, 115 ; 2003 Acts, ch 44, §57 Referred to in §275.23A , 275.25