First... I HAVE TO recommend switching him to a higher quality kibble. Science Diet just has loads of yucky ingredients, that are not going to help your pup to lose weight. I really like Taste of the Wild, is that available at any of your local feed/pet stores? Other good foods are Canidae, Innova Evo, Solid Gold, California Natural, Natural Balance, etc.

Diet foods are simply packed with higher amounts of carbs, and are a complete waste of money, IMO. Feed LESS of a high quality kibble. Add plain, canned greenbeans and/or canned pumpkin to his food, to make him feel fuller. Look into feeding raw meaty bones, to replace occasional meals; feeding Raw completely fixed my Border Collies weight fluctuations. For treats, give him baby carrots, apples, or small pieces of plain cooked chicken.

Most importantly, you need to exercise him as often as possible. Take him on a long walk, every day (if he isn't used to walks, start with short walks and build up). Play with him for 10-15 minutes as many times as possible through out the day. Take him to off-leash parks to run around and explore. Cutting back on food, and feeding premium foods, is going to help... but that might not do much, if he isn't getting enough daily activity.

Good luck. C: