Access the Settings menu, either by swiping down from the top of the screen and clicking the “gear” icon, or tapping the Settings icon directly. Scroll down to the “Backup and reset” option, and click. Play it safe and ensure the process completes before boxing up your return.
Note that this process should work for both phones and tablets alike.
To reset an iPhone, iPad, or iPod touch, access the Settings menu, then select General > Reset > Erase All Content and Settings. If you were using the Find My iPhone option, the device will ask your for your iCloud password to turn it off.
Apple OS X:
Macworld has an excellent in-depth primer on how to go about securely erasing your drive.
Windows 8 or 8.1:
Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings. (If you’re using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, click Settings, and then click Change PC settings.) Then select Update and Recovery, then Recovery. Then click Remove Everything and Reinstall Windows. You’ll also have an option to either quickly or thoroughly clean your data; if you’re the paranoid type, select “Thoroughly.”
Go to the Settings menu, then Update & Security > Recovery > Reset This PC. Make sure you select the option to remove everything, including your personal files. (You probably don’t need to apply the “scorched earth” policy of overwriting the data on the drives, although if you’re actually going to dispose of the PC, it’s not a bad idea.)
Swipe to access the Settings Menu, then click “About.” You’ll see an option to reset your phone.
Some devices also provide the option of remotely wiping them, or erasing their data, either using the native OS or a third-party app. But it’s far more reassuring to perform the reset yourself, with the device in front of you.
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