I have a friend who has a niece staying with him and he wants her evicted out of his house

So she is his tenant, in effect? If he complies with the rules in his jurisdiction for evictions, sure.

This is a very common question here. An eviction occurs when a resident refuses to leave after being given legal notice to vacate. So the first step is to give her written notice to vacate. The form of that notice depends on local laws (ANY question on law needs to include your general locale as laws vary by area.). Only after the resident lets the notice expire does is going to court for an eviction order required.