How can I find original Birth Cert?

Can someone help me find an original, sealed birth certificate?My husband was adopted at age 8 by his stepfather (his Birth Father died when my husband was 2) and his original birth certificate was sealed.How do we unseal it?All we can find now is his step father's name on his birth certificate.It's nice and all of the state to "protect" my husband's tender sensibilities, but this adoption was hardly a shock to him!!!And he wants to know about his birth father!!!

Thank you.