How do I change a custody agrement in new york state.?

My sons father and I share joint custody. At the time the agrement was signed , I also had no lawyer, I thought it was in the best interest of our son for him to be with his father more because I was working four to five nights a week. Now that i do not work as many nights I know that i will have more time for him and it would be in his best interest to be with me more. Where do I begin? People keep telling me this is going to cost 25,000 to 50,000 if he wants to argue and not agree to this. Where can i find resources so that I can start this.How do I change a custody agrement in new york state.?all you do is have him agree to the child spending that time that is now available, with you. If you guys are friends , and are not feuding, then this should not be a problem. You have not , because you ask not. Contrary to popular opinion, if you petition the courts for more time,it will only cost you time and, effort.All states are different, but I'm certain that a petition such as that will not cost money because you should be able to get the petition from the court clerk, or they can direct you where to get it.. good luk