Documentation:WordPress Basics/Change Your Username (How to)

Unfortunately, usernames cannot be be changed. However, if you wish to publicly display something other than your username please do the following:

• Go to Dashboard and under Users, click Your Profile

You will find Your Profile under the Users section of your blog's Dashboard.

• Under the Name section, fill out all the fields and then choose a name from the drop-down menu Display name publicly as

Your display name can be a combination of your username, first name, last name, and/or nickname.

• Click on the Update Profile button at the bottom of the page

Don't forget to save the changes by clicking the Update Profile button at the bottom of the page.