Ordinarily with respect to a child support modification application one submits the petition, the declaration, the income and expense report (net monthly) and back up documentation such as W-2's and check stubs attached to the declaration. The court makes the decision on the modification request based upon the net monthly income of both parents.The above information is served upon your "ex" and filed with the court. I suggest that you consult with a family law attorney to assist you in your endeavor. Do not give your tax returns. They are privileged.