Child Support Question?

Several years ago "we" were in court for child support. The judge said that if there is any change in income whether it be increase or decrease, we should go back. Several years go by and his job not only changed, but it now pays more AND I can no longer get payment on time like I used to!! Do I have to go back to the Original courthouse that the order was made or any courthouse? And will I need a lawyer for something like that? We are in same state, but not same city that the order was made! HELP!!!