If you delete the program you will not be able to open the tax files unless you have saved the returns as pdfs. Make sure you save them as pdf files. Returns prepared using desktop download software are NOT saved in an online account. They are stored only on your own hard drive or any back up device you use like a flash drive.
SAVE YOUR TAX RETURNS !
EVERY year before mid-October you should save a copy of your tax return as a pdf and print a copy of it for your records. That way you will not be searching online frantically when you need it for a lender, FAFSA forms, your next tax return, etc.
In order to transfer a past year return to the new return you need the tax file
NOTE: TurboTax and the IRS save returns for seven years. Returns older than seven years are purged.
And Turbo Tax will only let you reinstall or update the last 3 years. You can not reinstall 2020 or prior. So you might want to leave the old programs installed if you think you might want to open the tax data files in the future to look up anything or amend.
Also if you haven't done it, I would open each year in the program and save it as a pdf file, go to FILE - SAVE TO PDF so you don't need the program installed to view your return. Copy that folder to a flash drive or best yet is to burn it to a CD or DVD and then you will have a backup of them.