If you are not logged in and have forgotten your password, simply click on the Forgot Password? link under the Sign In button.
Enter your email address and click the Send Instructions button. You will receive an email containing the next steps to reset your password.
If you are already logged in and simply wish to change your password, you can do so from the Settings page. If you click the Account menu item, you can change your password using the form below. You will need to know your current password to change it from this form. Click the Save button when you're done.