How to Stop An iPhone From Syncing
Updating an iPhone is as easy as plugging it into your computer; by default, your iTunes application will automatically sync with your device. Syncing is the process by which information is exchanged between iTunes and Apple devices, including the iPhone. If you want to be more selective about what information is exchanged, you can stop your iPhone from being automatically updated and manually make all alterations.
Open iTunes on your computer and select the "Edit" tab along the upper toolbar.
Choose the "Devices" tab from the top of the screen.
Check the box next to "Stop iPods, iPhones and iPads from syncing automatically."
Click "OK" to save the new settings.
Plug in your iPhone. Any data that you want to be updated will have to be manually dragged from the library to the iPhone icon on the left side toolbar.