To change your Username -
Click on your name or image on the upper right of the screen. Select General Account Settings to reach the Account Management page. Click on the GENERAL tab and type in your preferred name. This name is displayed beside your system name.
To change your Username -
From Account Management page, click the PROFILE tab and change your screen name.
When done, remember to click the green Save Changes button at the bottom of each tab.
Have in mind that you can have your own name visible on C2 or your profile name.
You can change that by clicking on your name or image on the upper right of the screen. Select Public Profile, select Edit, and click on Show real name / Hide real name. All you have to do is save and you are set.