How to reset my Galaxy s4 Mini?

So basically, I dropped my phone and it's smashed all the screen, the phone still works but the screen is just black, cracked and the touch doesn't work either, so I can't use it, I'm getting an iPhone and my brother is fixing my samsung and he is having it, but the thing is I don't want him to reset my phone himself because he will most likely go through all my stuff, I don't mind pictures as I have nothing to hide but he will go through my messages and that's my private life, I'm 14 so obviously they'll be boys I have been texting. How can I reset the phone, like wipe it completely? Or if I take my sim out will my texts and contacts be off of it? Help

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