How do I remove profiles I am no longer using in the drop-down box?

From the main client window, open the "Settings" task panel.  Click the "Show the login properties window" link.  On the General tab of the AT&T Global Network Client - Login Properties window, select the Login profile you would like to delete then click the "Remove" button.  You will be prompted to ensure you want to remove the selected profile.  If you are sure you want to remove it, click "yes" and then click "OK" on the Login Properties window.