Your son will need to file a name change request with the court.
I suggest you have him wait until his 18th birthday.
Why?
It's much easier to do as an adult.
It'll make your life easier as his mom, coordinating school activities, health care, etc...
By the time he becomes an adult, it's entirely his decision, and you could offer to pay for it as a graduation present, or give him a choice about a down payment for a car.
It's an issue to a teenager, but a car is far more important than a name to an 18 year old boy.
I've found as a patent, stalking can be a great tactic.
But, for me, a NO, worked fine, too.
It's yoyr decision now, mom, it becomes his at 18.