Question: how do i sync my iphone with itunes without erasing everything?
Answer: Launch the iTunes application on your Mac or PC computer.
Go to "Preferences" in the "iTunes" menu on Macs or the "Edit" menu in Windows.
Navigate to the "Devices" tab at the top of the pop-up window, check the box next to "Prevent iPods, iPhones, and iPads from syncing automatically" and then click "OK."