hover your name in the top right then click on personal details and then you can change it in the "custom title" box, new member, well-known member etc. are the default ones that are given to you if you don't set a custom one. the badges/medals are for participating/winning forum contests/giveaways etc.
@Nathan Phillips its when you participate in forum competitions and or events/things that are happening on the forums. for example the thanksgiving and fourth of july ones were because i participated in a thread during that time.