How do we get the aggravated sexual assault to a minor charge expunged?

My husband was convicted of a sex crime. He served five years starting when he was 19 and wasn’t released until he was 25. After serving three years, the "victim" wrote a document that was seen in court. It stated the charge was false and all a lie but since he pled guilty like his lawyer told him to because he was so young and no one would believe him he still had to serve the whole five years. He has to register yearly as a sex offender and keep all his information updated.