Previously, we need to send a ticket to support and they will do that for us but now i find they permit to change it by myself from settings.
but i found these words under the edit form :
Consider carefully before changing your username as frequent changes are not permitted. Changes to your username may have an affect on URLs to your profile, items or services. History of username changes will be displayed on your profile.
What they mean with “History of username changes will be displayed on your profile.” ?