If you have not paid or registered, you should be able to clear and start over in the Free Edition or just clear and leave blank if you don't want to use TurboTax: https://ttlc.intuit.com/questions/2586254-using-clear-start-over-in-turbotax-online
There is no way to completely delete an account.
The Free Edition is only for very simple tax returns so if you are trying to downgrade to use it, you may not be able to complete your return with it. See this:
