Demonic Possession is when a negative entity such as a demon inhabits a person or object.
How to dispose of the demon possessing a human, animal, or living creature: Edit
If you are sure the person is truly possessed than bring them to a Exorcist or Saint. They can berid the demon or negative entity existing within the person.
Possession of Inanimate Objects: Edit
Demons and negative entities are known to possess not only people but inanimate objects, this is caused by Witches who want to harm society.