Every corporation of the character included in Code Section 14-4-40 having shares with par value, whether issued and outstanding or only authorized, may, at a meeting duly called for the purpose, by the vote of a majority of all its stock entitled to vote or, if two or more classes of stock have been issued, of a majority of each class outstanding and entitled to vote, including in any event a majority of the outstanding stock of each class affected, change such shares of any class thereof into an equal or greater number of shares of the same class without par value or provide for the exchange thereof pro rata for an equal or greater number of shares without par value, provided that all shares in any one class shall be changed or exchanged on the same basis; and provided, further, that the preferences, restrictions, and qualities of the outstanding shares so changed or exchanged shall not be otherwise affected nor the relative voting powers of the different classes of shares be altered.