Enter the email address currently attached to your paizo.com account on the password request page and you will be sent an email with a new, temporary password. Upon logging in with this temporary password, you will be prompted to create a new password.
If you receive the error message ‘That email address and password combination is not valid.’ when trying to use the temporary password, it's possible that when you copied the temporary password from the reset email, it added a blank space to either the beginning or the end of it when it was pasted into the password field. Typing in the temporary password manually should resolve the error.