I think you missed that Ford's OTA update system is currently broken. Have to go the USB route.I searched and this is the only thread I found that addresses this question. I can update and did it find on my SHO. But on the Mustang I keep getting, as does Fleco17 and the original poster the message:
"download incomplete, try again later"
The car is connected to my home wifi but won't download the Sync update. All of the other threads address how to update, but not this specific issue where it simply won't download on wifi. Unless there is some specific post that I missed in searching.
I've done the usb method and it updated to sync 2.3 from 2.0. It won't update to 3.0. I called Ford customer service and they said take it to the dealership for them to update it. Sorry, but they want to take your first born for doing this. I guess I'll give it longer and try again.