how can my fiance and I overrule a previous ruling?

if my fiance has a previous agreement with the father of her child, stating she cant move more than 60 miles from her current home. How can we get that changed if father has re married and insists on controlling where she can live. he refuses to let her move with her son, even though in the childs best interest i can provide far more than he can. I make nearly 90k a year he makes roughly 15k a year.. Would she and i getting married overrule the current rulling?