How do I erase my iPhone's data and settings?

Before you erase your device, we recommend you make a backup of your iPhone's data via iCloud or by connecting your iPhone to the computer you normally sync with.

Here is how you can erase your device BEFORE sending it to BuyBackWorld:

1. Tap the Settings (gear icon) from the home screen
2. Tap the "General" settings menu item.
3. Choose the "Reset": menu item.
4. Tap on the "Erase All Contents and Settings" menu item.

How to erase your device via iCloud, if it does not power on or AFTER you have shipped it to BuyBackWorld with iCloud

Sign in to icloud.com with your Apple ID (the one you use with iCloud), then click Find My iPhone.

Click All Devices, then select the device you want to erase.

In the device's Info window, click Erase [device].

To erase:

An iOS device: Enter your Apple ID password. If the device you're erasing has iOS 7 or later, enter a phone number and message. The number and message will be displayed on the screen after the device is erased.

If your device is online, the remote erase begins. A confirmation email is sent to your Apple ID email address.

If your device is offline, the remote erase begins the next time it's online.

You can also view Apple's FAQs here