The version of TurboTax you need to use is determined by the information/answers you have entered into your return. It may be that one of the forms you need to file is required in a higher version of TurboTax vs. the Free version.
This link will show you the forms that each program will file (scroll down and click on the Tax Forms tab):
https://turbotax.intuit.com/personal-taxes/online/free-edition.jsp
If you feel that you do not need the higher version of TurboTax, you can clear your return and start over to downgrade (as long as you haven't paid for or registered your account), instructions here:
https://ttlc.intuit.com/replies/4248526