N.H. Rev. Stat. Ann. § 195:16-a

Any cooperative school district may amend its existing arrangement or articles of agreement to increase or decrease the grades for which the cooperative school district provides education. If the cooperative district was organized pursuant to RSA 195:18, it shall proceed by amendment of its articles of agreement. The cooperative school board shall cease responsibility for the excluded school grades as of the date specified in the amended articles of agreement or the existing arrangement.