Any board desiring to change its method of election or its voting plan, or both, shall first prepare a plan of change showing the following:

(a) The territory, numbering and estimated population of each of the proposed member districts into which the school district will be divided, unless the proposed method is election at large.

(b) The territory, numbering and estimated population of each of the existing member districts of the school district, unless the existing method is election at large.

(c) The proposed voting plan.

(d) The existing voting plan.