When you and your ex got divorced, you had a very young child. The court did not consider what the child wanted, on the grounds that they were too young, but just decided on what was in their best interests. That meant they lived with you most of the time and saw your ex on the weekends.
Now your child is older and they've told you that they want more time with their other parent. They'd like to go live with your ex. What now?
First and foremost, it's wise to focus on communication. Don't avoid the conversation. Don't just shoot down the idea without considering it. Give your child a chance to talk and hear their side. Show them that you care and that you are listening.
Additionally -- and this can be difficult-- don't take the whole thing too personally. It can be hard to hear that your child wants more time with your ex because you hear that as if they want less time with you. Try to remember that they also love their other parent, and they're just trying to explore what is best for their own life.
You may also want to talk to your ex about it. This is not a decision you can make on your own. You have to find out if your ex is even willing or able to make these changes. The three of you may need to have a group conversation together.
As you work through this complex process, make sure you know what is involved in modifying your custody and support agreements. Your attorney can help you.