If you find that you may made a mistake and just wish to start over, you can use the Clear and Start Over feature to wipe all the information from your return. You may also wish to use this feature in order to downgrade from a higher version of TurboTax or if you no longer wish to use TurboTax. Please note that if you have already paid or registered your product, then you won't be able to clear and start over. You would have to create a new account or manually remove all the data.
Go to My Account -> Take Me to My Return -> Clear and Start Over. Here is an article with more information -
