Change user settings
You can change your name, gender, birthday and presentation as you wish by clicking Settings at the top menu.
You can also chose what other players will be able to see about you.
Changing your password
You can change your password with Settings > Password, and it will change directly. If you forgot your password though, you can reset it by trying to login, click "Forgot my password". You can there type in your email address you registered with, and you will receive an email with a reset verification. Click it and choose your new password.
Your password will always be encrypted, and no one (including admins) can see your password.
Changing your email address
It's possible to change your login / email address too. Click Settings > Email, and type in your new email address. You will receive a verification link to your new email address, and if you click it, the address will change. You will then have to relogin with your new user ID.
Yes, yes, you can unregister. And no, nothing will be saved (chat entries will not be erased), and you will not be contacted again. Promise!