Amendments of any city charter adopted under the foregoing provisions may be submitted to the electors by a commission as provided for a complete charter. Amendments may also be proposed by the legislative body of the city or by petition of not less than ten percent of the registered qualified electors of the city, filed with the body or official having charge of the city elections, setting forth the proposed amendment. The legislative body shall at once provide, by ordinance, that any amendment so proposed shall be submitted to the electors at the next election held in the city not less than sixty days after its passage, or at a special election held as provided for a charter. Any amendment approved by a majority of the qualified electors voting thereon, shall become a part of the charter at the time and under the conditions fixed in the amendment; and sections or articles may be submitted separately or in the alternative and determined as provided for a complete charter.