You would need to go back to the court and file a motion to reopen your divorce to modify the parenting order. There are several factors under the law the court must consider when looking to modify a custody order. If you had an attorney for your divorce, and you were satisfied with the services provided, you may wish to see if you can obtain a free consultation with that attorney to discuss your desires and that attorney would be familiar with the case background.
If you didn't have an attorney before, you may wish to consult with one to make sure you have enough grounds to give to the court in order to have custody modified.