How often do i feed my elderly indoor cat wet food?

I have fed my cat dry cat food all his life, he is an indoor cat and health if a little over weight. He is now 13 years old and starting to have trouble with hairballs and puking in my room. I want to switch him to healthier canned indoor cat food for old cats. He has always been able to eat whenever and how much he wants with the open food bucket but now i closed the dry food. My question is how often do i feed him a day from the canned food?