You can use the steps below to restore your device to factory settings and remove all settings and information. Depending on your device, it can take a few minutes to completely erase your data.
Erase your iPhone, iPad, iPod touch, or Apple Watch
You might need to enter your passcode and Apple ID password before you erase all content and settings.
To erase your iPhone, iPad, or iPod touch, tap Settings > General > Reset > Erase All Content and Settings.
To erase your Apple Watch, tap Settings > General > Reset > Erase All Content and Settings.
Erasing all content and settings on an iPhone 3G or earlier and iPod touch (2nd generation or earlier) can take several hours. Before erasing one of these devices, connect your device to a charger and leave it connected until your device resets.