Just joined. Can't change profile pic.

When I try to change my profile pic from the default placeholder pic, I get sent to the Registration Information page (which I've already clicked through).  I'm stuck in a loop and I can't get out.

It's not actually a "registration page", but the profile page. On that page, you can supply a profile and cover picture from "general information about yourself" -> profile picture.
Click here for more instructions on how to upload a profile / cover picture.