I just adopted an adult cat who was very attached to the last owner. How can I help him adjust?

Bribe the cat with food. Play with it a lot. My dog was attached to his owner but we got him to like us by playing with him and feeding him. Give the cat cat nip sometimes, they love it. Get the cat neutered when he adjusts a little. But if he starts to spray, NEUTER HIM IMMEDIATELY. Their spray smells disgusting and it will really upset your other cat.