Hello there,
There are different options available in account setting of your Profile to edit your visible or hidden contents.
Have a look at the tab of PROFILE within Menu bar of the Diwwan.
As account setting of the profile said "Username" is a primary key to login in DIWWAN system so its not possible for a user/member to edit it but admin can do it for him/her.
I think your concern is not USERNAME but DISPLAY NAME.
So instead of changing login name try to edit NAME option which is placed on second field/column of the system. So whatever you want to display for public add it within NAME column. Hope your problem will be resolved.
In case of any confusion or further help please feel free to ask.
Regards
Baask Admin