How do you switch from Deluxe edition to free e-file edition ?

TurboTax has 2 free products, so I'm not sure exactly which one you are asking about--regular Free Edition or the TurboTax IRS Free File Program.   So I'll tell you about both.  Read this entire long answer before making a choice to be sure you end up in the right product.

The regular Free Edition is for very simple returns and not everyone can use it.  Certain forms are not available in Free Edition and require an upgrade to Deluxe, such as one of Schedules 1-3, itemized deductions, etc.   Did you start in Free Edition and had to upgrade?    If you haven't already paid or registered, and if you are sure you don't need Deluxe, you can use the "Clear and Start Over" feature to choose regular Free Edition, but depending on the complexity of your return you may not be able to use regular Free Edition.  If you need to itemize deductions, for instance, or have one of the Schedules 1-3, etc., you won't be able to use it.   See this FAQ on some situations where one cannot use Free Edition:

FAQ:  Why do I have to upgrade from Free Edition?
https://ttlc.intuit.com/community/upgrading/help/why-do-i-have-to-upgrade-from-free-edition/00/26379

If you're sure you don't need Deluxe and want regular Free Edition:

FAQ:  How do I clear and start over in Online TurboTax?

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-onli...

The other free product (TurboTax IRS Free File Program) is fully-featured and can prepare all the usual forms and schedules.  It is even more powerful than Deluxe, if you qualify.  For example, it can prepare Schedule C, D, E, F, etc., and enter K-1. But one has to meet one of the qualifications to use.  See below:

To qualify for free 2019 federal and state tax returns through the IRS Free File Program delivered by TurboTax, you just need to meet one of these requirements:

• Your 2019 household AGI is $36,000 or less; or
• You qualify for the Earned Income Tax Credit (EITC); or
• In 2019, you served as active duty military (including Reservists and National Guard) with a maximum AGI of $69,000, and you have a military-issued W-2.

If you qualify for that program and want to use it, see these 2 FAQs:

FAQ:  What is the TurboTax IRS Free File Program?
https://ttlc.intuit.com/community/choosing-a-product/help/what-is-the-turbotax-free-file-program/01/...

and

FAQ:  How do I switch to the TurboTax IRS Free File Program?

https://ttlc.intuit.com/community/downgrading/help/how-do-i-switch-to-turbotax-free-file-program/00/...