First, I would cut back on the food if he is getting too much, a cup in the morning and evening should be sufficient. You might want to add a half of a can of green beans to one of his meals just as a filler so he doesn't feel cheated. Fresh fruits and veggies are acceptable but no grapes. Cut the pieces into smaller chunks so when you treat, you can give a few more but it actually is a smaller amount. Exercise is a must. I would turn up the exercise and if you are unable to take him out and play, walk with him. The weight will come off, and it's important to keep him fit so that lessens the chances of joint problems as he gets older. BTW, welcome to the forum. You will find everyone here will be glad to help you with suggestions and ideas. We have several seasoned breeders who really know their stuff and have a wealth of knowledge they love to share. Labby is one and she is amazing. So, again, welcome and don't be a stranger. PS We love pictures, so please post some of your boy.
You've gotten great advice. Just wanted to add: make sure you measure w/ an actual measuring cup and not a scoop. If you want to use his kibble as a treat, remove it from the next meal's amount.
I'm not sure I agree w/ the blanket statement that 1 cup, 2x a day should be sufficient. It obviously depends on the food you feed (calories), and the amount of exercise your dog gets. Mine can't hold her weight on 2 cups of food a day.