All usernames at RummyCircle are unique. Once a username is entered by the player, it can neither be modified by the player nor by the customer support team due to security reasons.
However, there is an exception to this rule: when the system automatically assigns a username to an account at the time of registration, the player will be given one opportunity to modify it. This is most often the case when the player's desired username is unavailable (already taken by a different user).
You can go to the My Account, tab on My profile and click on 'change username' to modify the same.
Once modified, the username would be permanent for the concerned RummyCircle account.