How can my husband and I change my son’s name and him to adopt my child?

In 2009, I conceived a boy with my boyfriend at the time. He was at his birth, signed the birth certificate, had me move into his parent’s house in another state so he could be there and provide for our son. His parents supported us, despite what he said, and he had a job. Our son was 4 months old when I found out his biological father was cheating on me with his previous girlfriend. They're married, housed and have a daughter now. I confronted him. He said it’s over, claimed our son was my brother’s (sick to my stomach still with that response) and he was done with us. He moved out of his parents. He left us there with nothing but awkward tension and struggle. I decide to move back with our son, (February 2009) with my family. He was mad we left and said the reason he can’t care for our son was he’s not his (which he is), I’m too emotionally hurt still to talk civilly and we were too far away now. He had his parents and wife speak for him when I called. His wife toyed with the situation and me horribly. His mom and dad would lie and say they were taking our son to see his dad. Really they kept him at their home without my son’s father ever being there. They didn't want to lose their grandson because their son didn't claim him or fathered him in any way. His parents would send clothes in the mail and letters to my son. My son’s father sent $200.00 total in the 1st year of our son’s life and just stopped. His last call was, October 2009 to inform me he’s done and we can kick rocks. I left him alone. I told his family what their son told me. I told them to talk to him about this now. I gave up! I changed my number and moved in with my parents without informing him of anything. Now, I’m married, own a house, and my husband has fathered my son since he was 2 years old. My son only knows my husband as dad. My son will be 7 May 26th. We want to end this! I don’t know where he’s located, or his phone number. I messaged his wife 8 months ago on Facebook about this but she didn’t reply.