If you got an iPhone or iPad from another user or if you are giving away your iDevice to someone else, it makes sense to delete your Apple ID associated with the iPhone/iPad completely. Erasing all content and resetting the iPhone is one way but here’s a complete method that lets you remove all traces of your Apple ID from your iPhone.
The Easy Method: the easiest way is to remove everything from your iDevice. To do this, all you have to do is go to Settings → General → Reset → Erase All Content & Settings. Then, Settings → General → Reset → Reset All Settings.
See also:
Erase all contents and settings on iphone
Delete everything from iPhone
