how to cancel itunes membership

What exactly do you want to do ? Only iTunes Support can potentially delete an account (which would also delete its purchases), if you no longer want to use an account then remove any personal info it (e.g. remove credit card details), cancel any auto-renewing subscriptions on it, and stop using using it

You can try contacting them via this link and see if they can/will delete an account : http://www.apple.com/support/itunes/ww