My sons father wants to sign over his rights. So how do we do this.

You can look at the other threads on this issue (there are plenty) but the short answer is you have to get a lawyer and go in front of a judge to see if it will be allowed.

If the judge will allow it, you get an attorney, write up a agreement and have the judge sign it, But do understand and let him know that you can still sue for child support, he may not be as willing to sign over rights after he learns she can still be forced to pay chid support.