I can't change the Apple ID?

Okay, so when my sister came into town she gave my dad her old Iphone 5s. And she also restarted it so it could be brand new when he wanted to use it eventually.
So recently, my dad was on it and he failed to pay attention to everything and thought that he would be able to change the email and stuff after when he wanted to.
And it won't let us. We tried to reset the phone and it just asks for the password. We have no way to contact my sister and I know she wouldn't just give us our password. Is there somewhere online we can go to fix it or do we have to go into the apple store

Apple SUCKS. SAMSUNG is AWESOME.

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