The sync process applies the updates that were done on your family site to your project in FTB, and then takes the changes that were done to the website.
Every time you sync the tree that was prior changed on the site, Family Tree Builder creates a backup of your project. The default number of backups to keep is 10.
Thus if your project was changed on the family site online, and those changes were downloaded to Family Tree Builder during the last sync, you can decide to get back to the previous version of your project.
It is possible to undo changes that were made after syncing your tree and downloading changes from the site, by restoring your project from the backup copy in Family Tree Builder.
In order to do so, please open Family Tree Builder on your computer. In the upper menu bar click on ‘File’ and select ‘Restore project'.
On the new window that appears, select ‘Restore from a file on the disk’ and click on the ‘Next’ button.
Select the appropriate Project (Family Tree) from the drop down box titled ‘Project’. Then select the appropriate backup to be restored from the drop down box titled ‘Backup to restore’ and click ‘Next’.