If there is a child support order issued by the court, you have to go back to court and petition for it to be terminated.
You will have to provide supporting evidence that it is no longer necessary, or that he is unable to pay, meaning you will both need to fill out financial reports and submit them along with the petition giving the reason, and appear before a judge. If the judge does not agree, the support orders will stand.
Unless and until the support orders are terminated, he MUST continue to pay, or he will be held in contempt of the court order. You cannot just tell him to stop paying, and have that be enough, and you cannot expect a judge to allow him to stop paying unless another person is being allowed to adopt the child, or some other unusual circumstance has made the support unnecessary.
You may go to the family court website or the actual courthouse, to get the paperwork to petition the court. There will also be a law clinic at the courthouse, where volunteers can help you fill it out properly and guide you in the process.