dissenting.
By reaching the result it does, the majority purports to rectify an ill-advised decision by the trial court of a sister state. It *535is not the function of this Court, however, to act as an appeals court for the State of Missouri, and the decision reached today does violence to the principle of full faith and credit and directly conflicts with recent precedent in this Court.
Appellant Joseph Poirrier and appellee Hazel Jones were divorced in the State of Washington in 1975. Pursuant to the divorce decree, appellant was ordered to pay support for the four children of the parties, who were given to the custody of appellee. Appellant moved to Missouri and did not pay the support as ordered.
Consequently, in 1981, appellee initiated a URESA action to enforce appellant’s duty of support and to collect arrearages. The action was heard in the Circuit Court, City of St. Louis. That court ordered that the Washington divorce decree be registered in Missouri as a local judgment and ordered appellant to pay support in accordance with the Washington decree. Additionally, the Missouri court entered a judgment against appellant for accumulated arrearages of $9,420, and ordered appellant to make monthly payments of $25 to appellee until the indebtedness was satisfied. No appeal was taken.
Appellant subsequently moved to Sheridan, Wyoming, and appellee initiated this action pursuant to the URESA and the UEPJA, seeking modification of the $25 monthly payment on the arrearages as ordered by the Missouri judgment. It was established at trial that all the subject children were emancipated. It was further established that appellant had paid his child support obligation except for the arrearag-es and that his payments on the arrearages were current, with an outstanding balance of $7,895. The district court’s order granted appellee a judgment for $7,895 and modified the monthly payments on the arrear-ages to $125 per month.
The district court lacked authority to modify the Missouri judgment in this manner. Regardless of how the majority characterizes the Missouri order on the arrear-ages, it was a final judgment for a fixed sum of money, with provision for the method of payment.1 Although the URESA provides authority for courts of responding states to enforce foreign support decrees and allows such courts to modify foreign support orders with respect to future payments, Bjugan v. Bjugan, 710 P.2d 213 (Wyo.1985), it does not provide authority for courts of the responding states to modify arrearages reduced to money judgments. We explicitly recognized as much in Bjugan, 710 P.2d at 218, wherein we cited Salmeri v. Salmeri, 554 P.2d 1244 (Wyo.1976), for the proposition that, once an arrearage becomes vested with the attributes of a money judgment, it is not subject to modification. We further said, “the fact that a final judgment for a fixed sum of money grows out of a divorce action does not authorize the courts to extend the time of payment or otherwise modify payments.” Bjugan, 710 P.2d at 219. Similarly, in Salmeri, 554 P.2d at 1248, we recognized that a money judgment on an arrearage registered in this state pursuant to the UEFJA, which implements the full faith and credit clause of the United States Constitution, is not subject to attack
except on grounds that would permit attack upon any other money judgment, such as want of jurisdiction in the court entering the judgment or lack of service so as to vest jurisdiction over the defendant.
Further, although the district court modified only the amount of the monthly payment, it clearly modified the judgment. In Bjugan, it was argued that a change in only the amount of the monthly payments ordered by the court of another state did not constitute a modification. We rejected that contention, stating:
To say that the order changed the amount to be paid each month but did not modify the original decree is nonsensical. Modification means to change, enlarge, or reduce; to modify is to change or alter in a quantitative sense. Black’s *536Law Dictionary (5th ed. 1979). * * * In our view any change in the amount, manner or method of payment constitutes a modification. If an order does not conform to the original decree, it is a modification.
Bjugan, 710 P.2d at 219.
Neither the URESA nor the UEFJA, therefore, provided the district court with authority to revise the Missouri judgment.2 The Missouri court, in the prior URESA action, gave full effect to the Washington decree, ordering continued support and calculating the arrearages. In reducing the arrearages to judgment, the Missouri court additionally provided for the method of payment. It may be that the Missouri court anticipated or intended that the ar-rearage payments should increase to a reasonable sum upon the termination of appellant’s monthly child support obligation and that, in an oversight, it simply failed to include such a provision in its order. This, however, is only speculation, and the judgment is specific as to the terms of payment. Appellee did not appeal the Missouri decision, and that judgment is entitled to full faith and credit as a final judgment for a fixed sum of money.
For the foregoing reasons, I respectfully dissent.
. Under similar circumstances, courts of this state have reduced arrearages to judgment and provided for the judgment to be paid in installments. See, e.g., Manners v. Manners, 706 P.2d 671 (Wyo.1985).
. The district court recognized that neither of the uniform acts provided authority to modify this judgment, and it invoked its equitable powers to increase the amount of payments on the arrearages. The equitable powers to grant relief from a judgment, however, exist only in the case of fraud, accident, mistake, or undue advantage of the prevailing party. Midwest Ref. Co. v. George, 44 Wyo. 25, 7 P.2d 213 (1932); 46 Am.Jur.2d, Judgments § 804 (1969). None of these grounds was alleged or found in this case. Further, an unjust judgment or order, by itself, does not provide grounds for relief under equitable principles — the aggrieved party must demonstrate a satisfactory excuse for not having made his claim in the original action and for not having used diligence in seeking relief. Paul v. Paul, 631 P.2d 1060 (Wyo.1981).