Del. Code tit. 22 § 305
The regulations, restrictions and boundaries may from time to time be amended, supplemented, changed, modified or repealed. In case, however, of a protest against such changes signed by the owners of 20 percent or more, either of the area of the lots included in such proposed change or of those immediately adjacent thereto extending 100 feet therefrom or of those directly opposite thereto extending 100 feet back from the street frontage of such opposite lots, such amendment shall not become effective except by the favorable vote of three fourths of all the members of the legislative body of the municipality; provided, however, that in any municipality of this State with a population in excess of 50,000 persons, the foregoing provisions regarding a protest shall not be applicable to any such change which is proposed in connection with the construction of federally assisted multi-family housing for the elderly and handicapped, in all instances of which such change shall become effective by the favorable vote of a simple majority of all the members of the legislative body of the municipality. The provisions of § 304 of this title, relative to public hearings and official notice, shall apply equally to all changes or amendments.
22 Del. C. § 305