what do you mean making a username? if you mean edit you can simply click on your profile and click edit and you can change your profile picture and name. But dont make it against the rules.

i think he/she means changing there username

@43, Hi. I do not understand what you mean. Please explain more.

go to your profile press edit and click on your name and make it into what you want, as long as the name is following the rules, and it should work.