There are two main categories of modification cases; first, a party may seek to have a financial obligation, such as child support, modified; or a party may wish to modify timesharing and parental responsibility.  

The first type of modification case is a child support modification.  Child support modifications should be sought when there is a "substantial change in circumstances" which would either increase or decrease the amount of child support to be paid or received by a party. 

Some events that may constitute a substantial change in circumstances are:
(1) the loss of a job;
(2) a substantial decrease in income; 
(3) a substantial increase in income;
(4) a substantial change in daycare/aftercare expenses for the child at issue;
(5) a substantial change in the health insurance expenses for the child at issue;