If you have already started your return you will need to start over to downgrade to a lower version of TurboTax.  You can perform this once you have logged in and are looking at your return.  Please click the My Account option then Clear and Start Over. Once you are on the page to select a new product the program will automatically offer you the version you used last year.  In the lower right corner, however, you will see an option to select a different product.