How do I terminate Indiana child support payments for child who is age 19?

If the case has two children then it is likely that the child support is an engross order.  For example, let's say that a case has two children and the child support is set at a $100.  Just because one child turns 19, the order doesn't automatically change to $50.  Instead a modification would have to be filed and the court would determine whether a new child support amount should be set because now the case only has one child.