How do you change your dogs meal if he loves his older food but he doesn't like his new food?

He'll get used to it. Don't expect it to be an instant hit. He'll get hungry and eat it when that's all that's offered. Also, I worked at a veterinary clinic where they would add a splash of hot water to a scoop of canned dog food and mash it up to make a "gravy" in the bowl, then add the dry and mix it up together.