accounts cannot be deleted. You can delete all of your posts and/or abandon the account. The easiest way is to just abandon the account by changing the password to some extremely long random string of characters that even you don't know.

You could also sell your account. You are a sr. member, you could sell your account for around 0.2 BTC and then you would make a profit off of it and someone else can use the account instead of letting it sit and take up space on the server.