It's difficult to delete an account due to the way forum software works these days:
Each account has an ID, and each forum post is associated with that ID in order to record who was the original author and stuff like that. Deleting your ID would simply mean that the author for your comments is no longer known.
Even more, nowadays databases are designed in order to enforce that referential integrity (you can't delete actually data if it's tied-up as a reference in other database tables).
Probably you want to go to
http://www.englishforum.ch/profile.php?do=editoptions and disable the email notifications for your account. That should do the trick.