The older versions of TurboTax probably won't even install on the newer operating systems, much less even run on the newer systems. But if possible before you remove the old versions, open the tax return and elect to do two things.
Print *E*V*E*R*Y*T*H*I*N*G*. Not just the forms required for filing, and not just the forms to "keep for your records". Print it all. That way if ever audited you will have worksheets and all to help you (and a potential auditor) understand how you achieved a figure that may be in question.
Also, elect to save everything in a PDF file and protect that file like you protect your social security number. If years down the road you need that old tax return for something and don't have a printout or have it in PDF format, then your just up the creek, without a paddle, in a sinking canoe with a hole in it as you run the rapids towards that granite cliff with the 1000 foot drop.
That's what I suspected. I didn't know if Intuit had a passthrough or backwards compatible set-up. Thanks for the quick response, Carl.
I see you're on a MAC. So if you have any issues with it, just post back here and @macuser_22 will see it since I've flagged him in this thread.
A given years .tax20xx file can only be read by that years software. I keep the software for at least 7 years. Although in most circumstances you can only amend for a refund the last 3 years, the IRS can go back 7 years for missing income, so it is good to be able to access the actual data file for those years.
Unless you are short on storage, there is no reason to delete the application or Applications Support files for that year.
TurboTax 2010 runs fine on the latest Mac OS.