The username of an account will typically be the email address that was provided when the account was created.
To view your own username, go to account admin>your details. Account Owners / Admins of a Company Plan can view the username of other users within their account via account admin>manage users.
Although it is possible for users to change the email address of a user, it isn't possible for users to change a username.
If you would like the username changed, please send an email to firstname.lastname@example.org or submit a support ticket confirming the user's current username and the new username you would like it changed to and we can sort that for you. Please remember a username must be unique.