Changing Account Name and Nickname
Your account name is the name that is associated with your account. Your Nickname can be set differently for different servers that you are a part of.
To change your account name, click on the pencil beside your name.
Click on Edit account.
You can now change your account name to something of your choice.
You might want to change your Nickname within a server. Left-click on your name in the server list- select change Nickname