A factory reset of your iPhone erases all of your content and settings, restoring it as well. However, you must take some extra steps if you plan to get rid of your iPhone.
What does a factory reset do?
As its name suggests, a factory reset will erase everything on your phone and return you to its original state. It erases all your photos, applications, accounts, videos – there will be nothing left. A factory reset takes several minutes. Once done, you will be prompted to configure your iPhone as new.
What a factory reset does not do is completely reinstall your iPhone software. If you troubleshoot your device and that a factory reset does not solve the problem, you can try Reinstalling the operating system of your iPhone.
However, if you plan to sell your phone or change platform, you must perform some operations in addition to the factory reset.
Disable Find My iPhone
If you reset your device because you want to sell it or give it away, it is essential to disable "Locate my iPhone". From iOS 7, "Find My iPhone" also serves as an activation lock. This means that if "Find My iPhone" is enabled, only you can set up the phone again. Fortunately, turning it off is easy.
Open the Settings app and tap your name at the top.
Tap iCloud> Find My iPhone.
Disable the toggle, enter your Apple ID password when prompted, and then press "Disable."
If you change platforms (from iOS to Android), you must also cancel the registration of iMessage.
If you change platforms, cancel the iMessage registration.
When an iPhone user sends a message to another iPhone user, Apple uses iMessage by default. If you switch to Android and you do not unsubscribe your phone number from iMessage, the iPhone Sender will still think you have one. Your messages will end up in "iMessage Abyss" instead of being converted to SMS / MMS and sent to the Android phone.
To unregister iMessage, open the Settings application, scroll to the screen, and then press "Messages."
Press the button next to "iMessage" to disable it.
Your phone number is now unregistered in iMessage and you can continue to reset the default settings. If you missed this step before you get rid of your iPhone, do not worry. You can go to Apple standalone support site and submit your phone number to be deregistered. You will receive a free SMS with a confirmation code. Enter the code and you will be ready to leave.
Once these items are eliminated, you are ready to reset your phone.
Perform a complete factory reset
When you are ready to reset the device, open the Settings application and then press "General."
Scroll down and tap Reset> Clear all content and settings.
If you have an authentication code, you will be prompted to enter it. Do it, then tap "Clear iPhone".
Press "Clear iPhone" a second time.
That's all! Your phone will process for several minutes. Once it is restored, you will be prompted to configure your iPhone as new.