How do I leave my religion?

I haven't believed in god since I was a kid and still believed in Santa Claus. But the thought occurred to me recently that I am still counted as a member of the church if I was baptized, am I not? I'm not really sure how it works, but I live in the US and was baptized before I could talk so it's not like I had a choice in the matter and that pisses me off ;p Anyways I was baptized Methodist and I think, possibly, Catholic, but I'm not sure. How would I go about leaving both? Google fails me.