Reset iphone 6

My cousin recently passed away and his daughter is wanting to use his iphone 6. But noone happens to knkw any off his info to login. Name and password. Sonia there A way to reset it so she can go im and either get anything off of it, or anyway at all that she can even use it? It does have alot of sentimental value to her ans i woukd love to help out at least in this matter. Please help!!!