You can change the email address you're using to log in in Personal settings - Email.
You can see your current email address at the top. Below you need to enter new email (twice) and confirm the change with the valid password. Once done, hit Save new email button.
To change your password, head over to Personal settings - Security. First, fill in your current password, then type the new one - twice. Minimum length of password is 8 characters. We recommend using a combination of uppercase and lowercase letters, as well as numbers. To save your new password, click Save new password button.