You can change your own nickname once every 28 days. Here's a quick link: https://fetlife.com/users/edit_nickname.
To update your username:
Remember, please make sure that your new nickname is between 2 and 16 alphanumeric characters (letters and numbers) and does not consist of any spaces or periods (dashes and underscores are ok though) - our computers scream "RED" on spaces!
You should also check to see if anyone on the site is already using the nickname you want. A quick way to do this is to type in http://fetlife.com/usernameYOUwant in the URL bar. If you are taken to your activity feed, the name is available. :-)
If you made a typo or your name was changed by accident, contact the caretakers and they'll be happy to help fix this for you. Please email them from the email address attached to your profile and include your current nickname and desired nickname. You can contact them at firstname.lastname@example.org.