The regulations imposed under the authority of this Division may be amended from time to time by resolution after the resolution establishing the same has gone into effect, but no such amendments shall be made without a hearing before some committee designated by the county board. At least fifteen days notice of the time and place of such hearing shall be published in an official newspaper, or a newspaper of general circulation, in such county. Such amendment shall not be passed except by a favorable vote of two-thirds of all the members of the county board.