From Online Manual
- Display Name - A member may choose a display name that is different to their username. The Display Name appears next to a member's posts in the forum, so it is the name that is visible to the public. After registering at a forum, the display name is usually set to be the same as the username, but you can change this in the section Profile > Account Settings. Change the text in the field Name and then click on Change profile at the bottom of the page in order to save.