A. A nonconforming use of a building or structure, or part thereof, may be changed to a use of the same or of a more restricted (residential considered more restricted than manufacturing for example) character, but may not thereafter be changed to any less restricted use.
B. Any part of a building, structure or land occupied by a nonconforming use which is changed to or replaced by a use conforming to the provisions of this title shall not thereafter be used or occupied by a nonconforming use.
(1980 Code § 36-40)