The lawfully existing nonconforming use of part or all of a building or structure, all or substantially all of which building or structure is designed or intended for a use permitted in the district in which it is located, may be continued subject to the following provisions:
A. The nonconforming use of part of a building or structure, all or substantially all of which building or structure is designed or intended for a use permitted in the district in which it is located, shall not be expanded or extended into any other portion of such building or structure, nor changed to any other nonconforming use.
B. If a nonconforming use of a building or structure, all or substantially all of which building or structure is designed or intended for a use permitted in the district in which it is located, is discontinued for a period of ninety (90) days, it shall not be renewed, and any subsequent use of the building or structure shall conform to the use regulations of the district in which the premises are located.
C. No nonconforming use shall be changed to another nonconforming use when such nonconforming use is located in a building or structure all or substantially all of which building or structure is designed or intended for a permitted use. (1985 Code)