Before selling your iPhone, you need to make sure that all of your messages, emails, photos etc. are removed from the device. This is to prevent somebody else from using your personal data against you.
Before deleting any of your files, your iPhone should have a backup. Your backup can either be iTunes or iCloud.
Using iTunes to Backup your iPhone
1.) Establish a connection with your PC and your iPhone. You can use the computer that you usually sync with your Apple device.
2.) In the left side of iTunes, look for Devices and choose your iPhone.
3.) Control-click or right click the device and choose Back Up.
Reminder: Make sure that you have already transferred your purchases from your iPhone to your PC before you select Back Up. This can be done through a right click on your device and by tapping “Transfer Purchases”.
Using iCloud to Backup your iPhone
If you decide to use iCloud as your backup, then you shouldn’t have to worry about anything for iCloud is an automated back up system that operates regularly. However, you can run iCloud before you delete anything on your phone to make sure that you have saved all of your files.
1.) Have a stable Wi-Fi connection.
2.) Tap on the Settings app of your iPhone.
3.) Go to iCloud and proceed to Storage and Backup
4.) If iCloud Backup is Turned On, then look for Back Up Now and tap on it.
Deleting all of the settings and files on your iPhone
1.) Go to Settings app.
2.) Choose General.
3.) Look for Reset at the bottom of the page.
4.) Choose the “Erase All Content and Settings” option by tapping on it.
5.) Enter your password if you have any.
6.) Read the prompt that would appear on your phone.
7.) Choose the ‘Erase iPhone’ button by tapping on it.
Unregister or unlink your Apple device
You are recommended to unlink your Apple device from its official website as well. This is to prevent the new user of your iPhone in using your Apple ID.
1.) Open your browser and enter the url: https://supportprofile.apple.com/MySupportProfile.do
2.) If you are not yet logged in, then carefully enter your credentials.
3.) Choose Edit Products.
4.) Select the x mark which can be found on the product’s right side.
5.) Choose Unregister.
Unlink your device from other websites as well.