The Moderators decided to let users create their own user title. That is the text that is displayed just under your user name next to your posts.
Use the "User CP" under Edit Profile. You won't be able to use words indicating you are a moderator or administrator of the forum, assuming you aren't one, but otherwise you're free to change it as you see fit. Forum guidelines still hold. There is a 30 character maximum length.
Also, I reset all titles that were already assigned to "Member"--without Junior or Senior--so you can just leave it that way if it works for you.