The function to change the username is not by default offered by the forum platform, because it's not a database-friendly action, since each time a user changes their username lots of queries are sent to the database to overwrite the username in all posts, private messages, messages that user wrote on other member profiles, as well as all the likes that user gave and received.
So, the only option to change the username is to ask me to change the username for you directly in the user table in the database. Anyone who wants to change their username please post your request in this thread with the desired username and I'd check its availability and change it.
Note: A member can change their username for a maximum of 3 times.