In ARDI-AR and ARDI-VE, there are two ways to set your collaboration username.
The first is simply filling in the 'Username' field when first connecting to your ARDI server. If you don't have a password, simply leave that part blank.
This username will then be used to connect to the collaboration server.
Clicking on your name (which appears in the top-right hand corner on any of the collaboration panels, shown as Username in the image below) allows you to change your name at any time.