To change your username, email or password, please go to your settings from the dropdown under your username and profile picture.
You can change your username one time only, from your Quizlet preferences. Just scroll to the "Username change" section, and click the big button. You'll need to enter a unique username and confirm your password.
One thing to note: your old name will always refer to your account. You'll be able to log in with either your old or new name. This means that nobody will be able to impersonate you by taking your previous name. quizlet.com/jalenack and quizlet.com/asuth are the same user.
If you log in to Quizlet with Facebook, you'll be asked to verify your Facebook account before you can change your username:
Email address and Password
On the settings page, you can change your email or password your email address and/or password: