I lucked out because, when I was in high school, I deleted my Facebook account when I was a sophomore. I joined back up when I started college, because I wanted to network.
For maybe one or two months after starting college, I was going by my birth name (it's unisex, but unfortunately used more for females than males). But when I got to the point that I wanted to change it, I just put up a post, emailed my teachers, and asserted myself as my current name.
Weirdly enough, I still get friend requests from people that went to my high school. It's really awkward, and I don't even know how they find me anymore, since I look so different.