You can change it. Click on 'My Profile', then look around the screen for a short horizontal white arrow. Hover your mouse over that arrow, and a new menu will pop up. In that menu, click 'Profile', and there'll be an option to change your Display Name.
Additional step if the Profile link isnt clickable or is not visible. Follow Mark's directions but change your zoom to make the page small enough that all the menu options show. Then you can click on profile. You can set your zoom back to normal once you're on the profile page.