Unfortunately you cannot delete or
close your TurboTax account. However you can delete all returns from the
account.
When you login to your account,
click on the trash can icon next to a return to delete it.
If you only have one return, it
won’t show the trash can. Click on the “Continue” button after “Start a new
2017 return” to create a blank return. Then select “Return Manger” from the
“Tools” menu on the top right. Now you should be able to delete your return,
leaving only the empty return in the account.