Go to owner.ford.com, register your vehicle, then download the latest update from the Sync support site.
https://owner.ford.com/tools/account/how-tos/keep-your-sync-up-to-date.html
After downloading the ZIP file to your home computer, unzip it onto a blank formatted USB drive, 8 GB or so name brand is best, FAT32 format. Then plug the drive into your Sync system and let it upgrade the software. Either have the battery on a tender or keep the car running during the update.