Use the "Forgot Password" link. The link is also available on the login page which can be accessed by clicking on "Login/Signup" link on the top-right of the page. If you have forgotten your username also, you can enter your e-mail id there. You will receive an e-mail with a one time login link. Use that to log into your account. You should change your password after then. To do that go to "My Account", whose link is available if you click on you username on the top-right of the page. Then click on "Edit Account/Change Password". Enter a new password on "Password" and "Confirm Password" fields and click "Submit".