The only way to downgrade your edition is by using the "Clear and Start Over" feature. Just keep in mind that all of your data will be deleted. More info below:
https://ttlc.intuit.com/replies/3288495
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***