You don't. But you can use the link link at the bottom of any page to write to the staff to request to have your account deleted.
If you intend to open a new account, please make sure to contact the staff first BEFORE you create a second account, as multiple accounts from the same IP address can get you banned (and it is much more work to get reinstated after a ban).
It sounds, though, like just not using the site anymore would suffice for you. You don't need to delete an account for that.