Wiping an iPhone or iPad in preparation for sale is a serious necessity and should always be done. Apple has made it easy for users to delete all information from its devices, allowing it to be clean for sale or given to someone else.
1. Go to Settings > iCloud and sign out.
2. Go to Settings > iTunes & App Store and sign out.
3. Go to Settings > General > Reset
4. After finding the Reset page, press Erase All Content & Settings.
5. Allow the iPhone/iPad to reset to factory settings.
6. Remove the SIM card.