You probably have forms or schedules not included in the Free version as part of your tax return. You must have a Simple form 1040 return only (no schedules except for Earned Income Tax Credit, Child Tax Credit and student loan interest) in order to qualify.
~37% of taxpayers qualify to file with TurboTax Free Edition. Click here to see what forms are included.
How to downgrade in TurboTax Online - Downgrade back to free to see what caused the upgrades. Also, see How to Review your Fees. If your TurboTax fees are higher than expected, you can reduce them by removing add-ons, see Help Removing Fees.