If your tax return has already been e-filed and accepted by the IRS, then it cannot be deleted.  If you need to make changes, an amendment will be necessary. 

an amend your tax return using Form 1040X.

To amend, find your situation below and follow the instructions.

TurboTax Online

TurboTax CD/Download

Here is an IRS link about filing an amended return.

If you have not efiled your return, you can use the "Clear and Start Over" feature to delete all your tax information from TurboTax by following these steps:

• Sign in to your TurboTax account and select the Take me to my return button.
• On the welcome back screen, in the left-side menu, select Tax Tools, and then Clear & Start Over (select the menu icon in the upper-left corner if you don't see this menu). 
• Answer Yes in the pop-up to confirm.

eventhough i have it through another agency

If you have already e-filed your return through another agency, you can use the "Clear and Start Over" feature to delete all your tax information from TurboTax by following these steps:

• Sign in to your TurboTax account and select the Take me to my return button.
• On the welcome back screen, in the left-side menu, select Tax Tools, and then Clear & Start Over (select the menu icon in the upper-left corner if you don't see this menu). 
• Answer Yes in the pop-up to confirm.