If you have a Khan Academy account and forgot your password, visit http://www.khanacademy.org/forgotpw. Enter your email, and a unique URL will be sent to that email address. Once you receive the URL link, click on it to be prompted to set a new password. (If you do not receive the email, check your spam folder).
If you are logged into Khan Academy already, visit https://www.khanacademy.org/settings