How do I go about getting child custody transferred?

My ex is having my child and we decided it would be best if we didn't get married. We discussed what we're going to do and we decided that it would be best if I had custody of our child since I have a good paying job and I could give her everything she needs.
The thing is we both have no idea where to start to transfer custody from her to me since we were never married. How soon does it have to get done? What has to be done? And how long does it usually take?
The child will be born in Wisconsin by the way, I don't know if that changes anything.

You are the father, you already have the legal right to custody.

Nothing needs to be done, although you might want to have a lawyer (family law) draw up a formal custody arrangement in case your admirably reasonable arrangement falls apart later.

you just file for custody when the child is born. if you are not requesting child support and she is ok with you having the kid, just do it so she can't come get it out of the blue one day...

This is a very simple thing to do. All you have to do is go to an attorney and sign some paperwork at any time through the childs life. If she wants to get out of paying child support all together then she will forefit all rights to the child, unless you can come up with another agreement between you 2 that gives the mother visitation rights. Whether or not if she can or cannot afford the child, the child still should have the right to get to know their mother, or father reguardless of who has custody. As far as where the child is born is what will determine what state you have to file the custody agreement with. I am getting ready to get custody of my son but, under different circumstances. My son is at the age that he can now choose who he wants to live with, and his mother will have no say in the matter finally. It's just a matter of signing some paperwork this summer with my attourney, and going before a judge, and its done.