The first election for commissioners where a Pleasure Driveway and Park District has become a General Park District shall be held at the next regular election for park district commissioners at which time two commissioners shall be elected for a term of six years to succeed the former president and two trustees whose terms have expired. In the succeeding biennial election three commissioners shall be elected to succeed the remaining former trustees, whose terms shall have then expired. These three newly elected commissioners shall decide by lot the term for which each shall hold office. The two drawing the longest term shall serve for six years; and the other shall serve for two years, and until their successors shall be duly elected and qualified. Thereafter commissioners shall be elected biennially for a term of six years to succeed the commissioners whose terms expire. Provided, in former Pleasure Driveway and Park Districts, where the trustees are appointed in the manner provided in Section 2-18 hereof, the first election for commissioners shall be held at the next regular election for park district commissioners after the expiration of the terms of the three or four former trustees (as the case may be) whose terms first expire. Said election shall be held at the time provided by the general election law at which two commissioners shall be elected for a term of six years to succeed said former trustees whose terms have expired. Two years thereafter an election shall be held at the time provided by the general election law, at which three commissioners shall be elected to succeed the remaining former trustees whose terms shall have expired. These three newly elected commissioners shall decide by lot the term for which each shall hold office, in the same manner as above provided for Pleasure Driveway and Park Districts in which the former trustees were elected by the voters.