The use of a nonconforming building or structure may be changed to another use permitted in the most restricted district in which that nonconforming use is permitted. Where the use of a nonconforming building or structure is hereafter changed to a use permitted in a more restricted district, it shall not thereafter be changed to a use which is not permitted in a more restricted district. The proposed use shall be subject to all the requirements applying to that proposed use in the most restricted district in which the nonconforming use to be changed is permitted.