How do I go about terminating my exs parental rights for our son if he's willing to do it. Do I go to a notary or what?

First it may not even be possible. But you will both have to hire an attorney and make a motion in court.

Remember giving up rights, does not stop child support, so he will still have to pay child support, unless there is a new partner to adopt the child.

If he does not want any rights, that is easy, he just never comes to see the child, and never calls, that is real easy and no court is needed.