Start the iDevice Manager and select "Backup" from the left menu.
The following view shows the existing backups created with iTunes or iDevice Manager.
If an empty list is displayed, no backups were found.
Mark the iPhone backup you want to open in Windows Explorer.
Copy either the displayed path and paste it in Windows Explorer or
Now select "Edit" Open Directory from the menu.
This will open Windows Explorer and display the backup directory at the same time.