Exit your apple Apple ID.
Go to Settings -iTunes Store and App Store, click on your Apple ID, and select Logout in the pop-up dialog box. (At present, the latest system is iOS 1 1.2. 1, so you should choose to log off. )
Turn off the function of finding my iPhone.
Find "Account and Password" in the settings, click iCloud, find "Find My iPhone", and then turn off this function.
Erase all content and settings.
Just click? Settings for iPhone-General-Restore-Restore all settings, and iPhone will be restored to factory settings. If you are a jailbreak user, you must first return to the state of not jailbreaking, and then restore.
Risk warning: Once all the information is deleted, it cannot be recovered. It is recommended to use iTunes for backup first, so that you can restore it immediately after importing a new mobile phone.
reference data
How to clear the data when selling old Apple phones? . Zhihu [citation time 20 17- 12-29]