Remove your iPhone, iPad from Find My iPhone, and iCloud so you can upgrade to a new device, franchise it, or sell it to someone else.
Earlier we showed you how to
Step 1 : Reset your device to airplane mode, or turn off all Wifi, 3G internet.
Step 2 : Start Find My iPhone on the device or download it
Step 3 : Find and select the name of the device you want to erase.
Step 4 : Click Remove on top right hand to delete.
Step 5 : One more window pops up confirm the Remove button again.
So you have successfully erased your iPhone, iPad from Find My iPhone and iCloud right on your mobile device without using a computer.
Image source : internet