To disable completely the automatic sync in Family Tree Builder (FTB), please do the following:
1. Click on ‘Tools’ from the upper menu bar and select ‘Options’.
2. On the window that appears, click on ‘Sync’ on the left hand side.
On the right hand side, set the Parameter ‘Sync Projects automatically to my site’ to ‘No’.
3. Click on the ‘OK’ button to save your settings.
If you only want to turn off the automatic sync of a specific project, please read the following: How can I turn off the automatic sync of a specific project in Family Tree Builder?