Hi,
There is no option to delete your account.
Once you've paid or registered, we're required to store copies of your
return. Just use the original account and let the other one go
dormant. You can also clear the information from your
unused account using the "Clear and Start over"
feature.
For further information you can refer to the
following link:
https://ttlc.intuit.com/questions/1899886-can-i-delete-my-tax-return-in-turbotax-online