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1) Select Settings, then select General.
2) Then select, Reset.
3) You will be presented with many options, but the option for a full erase of the iPhone is "Erase All Content and Settings".
4) Select "Erase All Content and Settings"
4) A confirmation window will appear explaining that this procedure will erase the device of all of its media, data, settings, and will take about 1 hour to complete. Once this procedure stops, DO NOT try in disrupt or you may damage the iPhone.
5) Select Erase iPhone.
6) A second confirmation window will appear, again warning you that the data will be erased.
7) Select Erase iPhone.
8) The device will reboot and a status bar will appear. Allow the device to finish the erase procedure before removing it from its power source.
After the iPhone is done erasing, it's ready to be packed up and sold. (Our generously handed down 
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