How do i completely delete my account?

In TurboTax Online, you can clear and start over as long as you haven't paid or registered yet (free users are asked to register their accounts before they file). More info: https://ttlc.intuit.com/questions/2586254-how-do-i-clear-and-start-over

If you want to deactivate your account instead, you'll have to send a message to Customer Service (they'll give you a case number and tell you what to do next): https://support.turbotax.intuit.com/contact/