Try http://www.wikihow.com/Reset-Your-Android-Phone first.
After that you should be fine. I only do the hard reset on phones that don't work. ( https://www.google.com/search?q=Samsung+S4+Mini+Factory+Reset&ie=utf-8&oe=utf-8 )
We have just bought a Samsung Galaxy S4 Mini from a friend.
How can we easily get rid of all his data?
Factory reset?
Thanks guys

Chowhound
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