A nonconforming use may be changed only to a conforming use as provided in the applicable zoning district regulations, and, once changed to a conforming use, no structure, building or land shall be permitted to revert to a nonconforming use. For purposes of this section, a change is not effected by either normal repairs and maintenance for upkeep purposes or the provision of modern instrumentalities necessary and helpful to reasonable continuation of the nonconforming use, which instrumentalities, either by nature or extent, do not act to change the nonconforming use to a different nonconforming use.