The information contained on your iPhone 4S is your own and should not be left on the phone if you decide to sell it. If you do not take the time to remove your personal information, files, music, pictures, and other data, there is a possibility it could remain on the phone. The person who purchases your phone will be able to access any data you did not remove. Even if you know the person you sell the phone to, it is still worthwhile to protect your information.
To remove your personal information and other data from your iPhone 4S before you sell it, you need to complete a backup and restore. The two different options you can use involve either connecting to your iTunes service from your iPhone, or connecting the phone to your computer and using iTunes on the computer. Both methods are not difficult to use for completing the reformatting process. If you are using the iTunes online service, once your backup is complete, you run the restore right from the phone by selecting “Settings”, clicking on “About” and choosing “Restore to Factory Defaults.” You are prompted to confirm whether you really want to perform this operation.
If you decide to use your computer to complete the backup, the process is slightly different. After connecting the phone to the computer, start iTunes. Once the app opens, select your iPhone from the list of devices and choose the restore option. You will be prompted to perform a backup, and then asked to confirm if you want to proceed with wiping the data from your iPhone.