At this time, it is not possible to change the username of a Kraken account.
If you would like to change the username because you feel it is not secure enough (perhaps it is too easy to guess), we recommend that you open a new account.
If you create a new account, you can verify that account using the same information and documents you had provided for your original account, if they are still valid.
Note: If you create a new account, you will not be able to transfer your current account's assets directly into the new one.