Can I upgrade from TurboTax Online edition to Desktop Edition?

That would not be considered an upgrade as it is a different version of the software. You would need to purchase the download version please note that it is only good for Windows computers and no mac. 

Thank you for choosing TurboTax.

I purchased the online version at a retail store and was assured by them that I could download the desktop version.  Clearly this is not true.  I have not activated my online version, yet I appear to be able to start a new return. I have definitely NOT started a return so is there anything you can do at your end?

Thanks.

@AndrewYvonne If you have purchased a wrong year for TurboTax Desktop you can submit an online Refund Request and purchase a correct version directly from TurboTax website.

Thank you for choosing TurboTax.