How do I go about adopting my wife's daughter

my husband and i would like him to adopt my daughter fiona also. he and i met when i was preganant with her, he has been taking care of her for 4 years now we have had other children together and we would really like to know how we can get this stuff started.fiona's father is in the army and half the time i can not get a hold of him he has said he would like my husband to adopt but then he changes his mind. he is no help at all. we raelly would like this to happen can any one help?:confused: