Press Windows+R on your keyboard to bring up to the Run dialog. Input cmd into the Open field and click OK to launch Command Prompt.
Navigate to the MobileSync directory by inputting the following command and pressing Enter.
cd "%APPDATA%Apple ComputerMobileSync"
Rename your old backup folder using the following command.
ren Backup Backup_Old
If you haven't created a new directory to store your backups please do so now.
Input the following command to create a symbolic link to your new directory.
mklink /J "%APPDATA%Apple ComputerMobileSyncBackup D:tempBackup"
You can use Windows Explorer to verify the symbolic link was created. Notice the arrow at the bottom left of the icon.
Test out the change by performing a backup with iTunes and verifying that your files are backed up to the new directory.