How do I Delete my existing apple account

You can't delete an account but you can change the email associated with an account.

http://appleid.apple.com

Read here:

http://support.apple.com/kb/HT5621

Apple ID: Changing your Apple ID

http://support.apple.com/kb/ht5621

Using your Apple ID for Apple services

http://support.apple.com/kb/HT4895

Apple ID: What to do after you change your Apple ID

http://support.apple.com/kb/HT5796?viewlocale=en_US&locale=en_US

iTunes Store: Associating a device or computer to your Apple ID

http://support.apple.com/kb/ht4627

iOS: Changing the signed-in iTunes Store Apple ID Account

http://support.apple.com/kb/ht1311

 Cheers, Tom 😉