Anyone who creates a new community account gets a generic user name as: userXXX. A new user can change the generic name within 7 days from the creation date by going into user preferences from the upper right corner, then selecting the "pencil" icon next to the existing user name:
For accounts older than 7 days, the username cannot be changed without the intervention from one of our community administrators. In that case, the best way is to tag @support_team and one of our admins will make the change.
