Before you get rid of your iOS Apple iPhone device, make sure that you’ve removed all of your personal information. Follow these steps to protect your data and get your device to its factory default state for the new owner:
Go to Settings > General > Reset, then tap Erase All Content and Settings.
This will completely erase your device and turn off iCloud, iMessage, FaceTime, Game Center, and other services.
If you’re using iOS 7 and have Find My iPhone turned on, your Apple ID and password will be required. After you provide your password, the device will be erased and removed from your account so that the next owner can activate it.
Contact your carrier for guidance on transferring service to the new owner.
When the device is turned on for the first time by the new owner, Setup Assistant will guide them through the setup process.
Important: Do not manually delete contacts, calendars, reminders, documents, photo streams, or any other iCloud data while signed in to your iCloud account, or the content will also be deleted from the iCloud servers and all of your iCloud devices.
If you no longer have your iPhone
If you didn’t follow the steps above before getting rid of your iPhone:
Ask the new owner to erase all content and settings as described above.
If you’re using iCloud and Find My iPhone on the device, you can erase the device remotely and remove it from your account by signing in, selecting the device, and clicking Erase. When the device has been erased, click Remove from Account.