If you don't know your password simply enter your e-mail address on the login page and click the button that says "E-mail me a password."
You will be e-mailed a temporary password. When you login with your temporary password you will be invited to create a new password.
If you have registered but have not received the e-mail message to confirm your e-mail address, first click here to request a new one.
If this doesn't help you will need to contact info @ wikitree.com (remove spaces) and they will help you secure your account.