You can downgrade using the Clear and Start Over feature https://ttlc.intuit.com/questions/2586254-how-do-i-clear-and-start-over but bear in mind that the different TurboTax "flavors" handle different tax situations and their associated forms.
For example, if you want to downgrade from Deluxe to Federal Free Edition and you're itemizing (Schedule A), you can clear and start over with the free edition, but once you enter your itemized deductions in the free edition, you'll be asked to upgrade to Deluxe.
Here is a short list of some common tax situations and the online products that now uniquely support them:
Itemized Deductions (Schedule A/1040)- Deluxe, Premier, and Self-Employed
Capital Gains or Losses (Schedule D) - Premier and Self-Employed
Rental Income (Schedule E) - Premier and Self-Employed
Profit or Loss from Business (Schedules C-EZ and C) - Self-Employed
If you are looking at TurboTax Federal Free Edition, keep in mind that this version is intended for taxpayers with very simple returns (Form 1040EZ filers with the standard deduction), for example first-time filers and students.
