This is how to change what's under your name - go to My Profile and click Edit Details. In the second box you'll see this text below and you can then type what you choose. There's limited space. You then have to scroll all the way down and press SAVE otherwise it won't do it. Hope this helps.

[QUOTECustom User Title This is the title that appears beneath your name on your posts. Check the 'Reset' box if you wish to use the default title for your usergroup and post count.]