Accounts cannot be deleted the same way that you can't delete a bitcoin address. Once you use your address to do a transaction it's there for posterity in the blockchain. Steemit.com is a website that interacts with the Steem blockchain. I am not sure but I think that you can edit your posts so that the content is erased. This will make the content no longer visible in the website however it can still be viewed in the blockchain if someone is willing to look for it.