What exactly are you asking? How to relinquish your rights to your child or how to seek custody and/or visitation? If you want to relinquish your rights, I think the mother has to petition the courts to have your rights terminated...and her husband has to be willing to show that he will support and raise the child. If you want visitation or custody, get a good lawyer, or paralegal (as they cost less) and file for visitation...of course be willing to begin paying child support soon after as this may push the mother to begin wanting it.
I am not a lawyer..please seek the counsel of a professional.