You would have to bring a legal action in the appropriate court (family or chancery court) and in the action, ask the court to modify the support order. You will file you legal papers and serve them on your ex-spouse, who is legally entitled to notice and who gets a chance to object; you will then have to prove in court, to the judge, that you are entitled to the modification. You may not win, but you always have the right to file the action and try, even if your ex does not want to discuss matters.