If I can't upgrade my old Macbook Pro to OS 10.9 or later, and decide to buy a PC, can I change my download to PC rather than Mac without having to pay again? And how would I do that?

[Opus 17 · Accepted solution]

If you become a subscriber to turbotax Advantage, you will automatically get both downloads each year.  If you bought the program separately, you will need to contact customer support to make the switch.

Also note that next year, turbotax will require 10.11 (El Capitan) or better, so if you don't or can't upgrade that far or farther, it may not be worth the bother this year.  I just upgraded my daughter's MacBook Pro from 2008 to El Capitan and it works fine, although that's as high as her model will go.  My MacBook Pro is from 2010 and runs Sierra just fine.