Your registered e-mails are used by Foswiki for sending you e-mails, include notifications of password changes.
You change your email address by setting the form field called Email in your user topic. If this form field does not exist it will look for a line like this:
* Set Email = user@example.com
If your old e-mail addresses are all invalid (you can't receive mail there any more) and you have forgotten your password, please contact rbg@in.tum.de for help.