how can i change my user name ?
Click on your icon/avatar:
click on your avator/icon in the pop-up dialogue:
This opens your profile where you can manage various things.
This is the view of your profile that I can see as a moderator. The Admin
button is probably not visible for you, maybe some other options are
also invisible.
Click on Preferences:
This will open this view, defaulted to the Account tab, you may see
more/other/less details since it is your user profile. The other tabs
contain other settings.
Edit your name (1), Click on Save Changes (2):
