As I already said (at least 3 times), it’s not possible to change or edit username.
@clarusgames (and to all who have this trouble, 'cause I did, for at least a year) – if you see the “re-send validation e-mail” at the bottom just above the save button, click it and validate your email (mine did NOT come to me the first 2 or 3 times I tried this last year, but it did work today).
Once you have validated your account with that email link, the Account Info screen changes and will finally allow you to change your username.
Hope that helps.
Thanks, you are right, but I am pretty sure I confirmed my email address last year. Anyways, it works now.
Confirmed working here! NOTE: You do have to authenticate your account via email before your able! Have fun! :)