Where a lawful structure exists at the effective date of adoption or amendment of this Code that does not conform to the terms of this Code by reason of restrictions on the area, lot coverage, height, yards, its location on the lot, or other zoning requirements concerning the structure, such structure may be continued, regardless of any change in tenancy, ownership, or management, so long as it remains otherwise lawful, subject to the following provisions:
(1) A nonconforming building or structure shall not be enlarged, extended, constructed, reconstructed, moved, or structurally altered except in a manner that conforms to the requirements of this Code;
(2) A nonconforming building, structure or portion thereof may be altered to decrease its nonconformity;