I faced with the problem. I can't delete my account cuz I registered by Facebook(
Then don't...
Similar to Facebook, you cannot completely delete your account, however you can deactivate it:
http://support.italki.com/entries/21680464-How-do-I-delete-my-account-
When you deactivate it, information about you will become unavailable to the public(sometimes it may take a while for it process), so people cannot search you.
However, the information is still saved by italki. They save it incase you change your mind and want to reactivate your account.
Hope this helps.
-Lou
I guess we are not allowed to do.