In order to modify a child support order, there must be a substantial change in circumstances since entry of the last support order. Examples of a substantial change in circumstances that would warrant a modification can include: a previous order that is more than three years old and that there is a 15% disparity between the support ordered previously and the current guideline support amount, a substantial involuntary decrease in the income of one or both of the parties, a substantial change in the needs of the child or children, or a significant change in the custody or visitation arrangement.