Welcome to the forum. You can follow the steps for forgotten password and then enter any email addresses you have (your email address can be used as your username) until you find one that works.
However if none of your email addresses work and you can't remember what email address you put in to make your first account then you'll need to pop onto live chat and see if they can track it from your other details.
You can get to live chat from the Contact Us page
(expand the Anything Else section at the bottom for options)
PS there isn't an option to delete your account as such, you can ask live chat to deactivate it by removing the payment details from the account though.