I completed my taxes, and am trying to review. TurboTax is now telling me that the product I upgraded to isn't allowed bc I'm a nonresident. How do I fix this?

Unfortunately, once you have upgraded or added features to your TurboTax return, there is no way to downgrade or remove the extra features. You would need to create a new return to go back to the original product. 

To start a new return, select “Start a New Return” from under “My Returns” in the top left corner. Once you have started your new return, you can select “View All Returns” from under “My Accounts & Returns”. Then delete the unwanted return by clicking the small Trash Can next to it or “Delete” under the return’s name.

Please note that neither Assist & Review nor Full Service can help with Non-resident or expatriate returns.