Your APAN profile is how people will identify you within a group. Once you've registered, complete your APAN Profile.
There are a couple of ways to update your settings, based on what you are trying to do.
The display name is your identity on APAN; it is displayed on the top right of the page and where your identity is shown on within APAN. The display name on the other hand can be changed. By default, your username will be used as the display name, unless you update your Settings within your APAN Profile.
Your profile's tabs (activity, group, etc.) are set by default. You cannot change these tabs unless you have permission.