Your Profile name is the name displayed on the site when you add any content. Currently this is only on comments you have posted, but in the future this will also include posts and pages.
To change your displayed Profile name to something different from your username, click on the Profile menu to the left.
1. The Profile menu.
2. The nickname section is where you can change what your profile will be called, once you have chosen a name, use the drop down box below this to select it. Click on Update Profile at the bottom of the page.