You have to ask Amazon how to download it. Look for download instructions on the Amazon web site or in any messages that they sent you. TurboTax is not involved in the download process when you purchase from Amazon.
One user said...
Go to Your Account; then Digital Games and Software (under Digital Content and Devices section at the bottom middle); your TurboTax purchase should show there under Downloads and Codes; the license code will be the 16 digit code next ot "Activation Key". Hope this helps!
Amazon article on how to download software,
http://www.amazon.com/gp/help/customer/display.html?nodeId=201380160
amazon.com/gsl/
GSL = Games and Software Library.
There used to be a link after you logged into your account to this, but I cannot find it anymore, and Amazon tech support is useless in telling me how to find it again.
To download your TurboTax software from Amazon, please click here for instructions.