For the purpose of promoting the public health, safety, morals, comfort and general welfare; conserving the value of property throughout the city; and lessening or avoiding congestion in the public streets and highways, the Council may, from time to time, in the manner hereinafter set forth, amend the regulations imposed in the districts created by this chapter. The chapter may be amended; provided that in all amendments adopted under the authority of this section, due allowance shall be made for existing conditions, the conservation of property values and the direction of building development to the best advantages of the entire community, before the adoption of such amendment.