My new macaw has really long claws from neglect from past owner how do I trim them?

Dreamer was a Bday gift to me{he is 8 years old} . His past owner has allowed his claws to become very long and sharp among allowing some behavioral problems. We have bonded well and i am working on his biting issues and fears. He now has a sandy perch but his claws are turning my arm into hamburger.