If your account login is via your Facebook or Google account, your password is the same as what you use to log in to those services. You can reset your password directly through Facebook or Google.
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 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 your Settings page.
Please remember to click Change password to save the changes.