How do you shrink a 100% cotton t-shirt?

I have a t-shirt, and it's a typical one you get from schools, clubs, etc. Problem is, it's a LARGE and I am like the skinniest person ever! I've heard of the logos getting ruined and stuff, and I don't want that to happen... How should I shrink it? Without a seamstress? And please don't say for me to get another size.... Thanks! (: