My wife's ex husband doesn't really take care of his son. He doesn't call or anything. The only thing that we get is approximately $45 every 2-3 weeks but that amount varies. I on the other hand have been providing everything for my wife's son even before we got married since her son was about 3 months old. Ever since I have provided food clothing well everything from dippers to health care and the only thing his bio father provides is gas money because that's the only thing $45 every other week is good for. The relationship between me and my wife's son is the same as a father and son relation. So my question is, I am a marine stationed in ca and his bio father is in Pennsylvania I have provided everything for my step son and his bio father doesn't even call, how do I go about to adopt him and change his last name to mine? And what would happen if he does not agree to it? What would I have to do?

Hire an attoreny, petition for this in court, the biological father will have to sign to give up his rights and agree to it.

To change the child's last name, the bio father would have to consent... this can be done without you adopting the child.

To adopt the child, the bio father must reliquish his parental rights to you to allow for the adoption. You are not going to be able to file abandonment on him because regardless of how little the amount is, he sends child support somewhat regularly... in the courts eyes, that is a form of "involvement".
If the bio father refuses to reliquish his parental rights, the mother could petition to have his rights terminated. But it will be an uphill battle all the way if the biofather fights this. In the end, it will be up to the judge.

Get an attorney and file for adoption. The attorney will handle the bio father's relinquishment of rights. Since your adopting the child will relieve him of having to pay child support (even the pittance he's paying), I doubt if there will be a problem.