Change Devices preferences in iTunes on PC
In the iTunes app on your PC, use the Devices pane in iTunes preferences to view and delete device backups, choose syncing options, and more.
To change these preferences, choose Edit > Preferences, then click Devices.
Display the device’s serial number in the list of device backups that are synced with this computer. Encrypted backups are identified with a lock icon.
Delete the selected backup. All backup files are deleted and can’t be recovered.
Prevent iPods, iPhones, and iPads from syncing automatically
Prevent devices from automatically syncing with this iTunes library when a device is connected. To sync a device, click the Sync button when the device is connected.
Warn when data on this computer will be changed
Choose the amount of changed data that will set off a warning when syncing to a device changes a designated amount of data on your computer.
Forget All Remotes
Disconnect all devices from your iTunes library.
This option is only available when you used the iTunes Remote app to pair an iPhone, iPad, or iPod touch with a specific iTunes library.
Reset Sync History
Reset your sync history so that the next time you sync, you’re asked to merge or replace information. (It won’t delete any synced information.)
This option is only applicable when you’re having trouble syncing your iPhone or iPod with iTunes.