If you know your current password, just login as normal view your Profile, and click the 'Edit your profile' link.
If you don't remember your password, use the 'Forgotten Password' facility, to change your password. You will need the original email address you signed up with.
If you don't remember or are unable to access the email you have setup on your account, then you will need to use the Contact Us link to get help from a volunteer Team Member.