If you've purchased a new iPhone and wish to retain your data from your previous device, you can do so by backing up the older device's content and transferring it to the new iPhone. According to Apple, the backup process for the iPhone occurs whenever the device is connected to the computer and stores backups based on the date they were saved to the computer. When transferring your data from one iPhone to another, any information that was previously on the new iPhone will be replaced.
Connect the iPhone to your computer using its USB cable.
Right-click the "iPhone" tab located in the source pane of iTunes (the side menu), and click "Back Up."
Click "Eject" on the "iPhone" tab and remove the docking cable from the older iPhone.
Insert the docking cable into the new iPhone and click the "iPhone" tab in the iTunes' source pane.
Right-click the "iPhone" tab and click "Restore from Back Up." Select the backup date and click "Continue."
Click "Eject" in the source pane to disconnect the iPhone.