As far as I know, "newbies" can't change their profile picture, and you are a newbie right now.
You must become a "normal" member to be able to change it.
In order to become a Normal member you must have been a member for at least 7 days and have 10 or more posts.
In other words, you're a member for more than 7days, so all you need to do is to reach 10 posts. Then you'll become a normal member, and then you'll be able to change your profile picture from "Edit profile & settings" button (it's on the left top side of the site).