I looked up the food and caloric content and 2 cups doesn't seem like too much food, but you could decrease by a half cup.

If you decide to switch food, I highly recommend using the Pet Nutrition Alliance calculator and the actual calorie content of the food rather than following the bag guidelines, which is usually overestimated.

I wonder if he's getting food somewhere else. How many treats is he getting? Is there food that is accessible to him when you're away? Does he steal from the trash? Retrievers and labs are basically food-seeking hoovers and will find any and all things edible (and some things inedible). And we as humans tend to over-treat because we love our dogs and food makes them happy.

An easy way to keep track of treats is to calculate how many he can have while staying within his calorie count for the day, then keep that amount in a separate container and refresh as needed every morning. That way you aren't just reaching into an endless bag.

Exercise will definitely help every dog stay happy and will help a bit with the weight, but food control is where it's at. With your regular walks (Is it 20-30 minutes per walk? If he's getting total 45 minutes to an hour of walking a day, that's a great start) and food monitoring, he should drop several pounds in a month or two, and then you can start building up exercise. Swimming is great for the joints. How are they off-leash? Off-leash on softer ground (grass, dirt) is a lot easier on then because they can start/stop as needed rather than pounding the pavement at a set pace. I'd also talk to your vet about how to read signs of pain and ways to manage it before it gets any worse.