N.H. Rev. Stat. Ann. § 651:66

The supervising agency, or the offender who has been sentenced to pay restitution and has not inexcusably defaulted in payment thereof, may at any time petition the court which sentenced him for a revocation of any unpaid portion of the restitution. If the court finds that the circumstances which warranted the imposition of the restitution have changed, or that it would otherwise be unjust to require payment, the court may revoke the unpaid portion of the restitution in whole or in part, or modify the time and method of payment.