Help!!! My cat is over weight

I have a brown,black, and white tiger cat.....He is about a year and a half old. He is a very big cat and now weighs 19lbs. I want to put him on a diet but im not sure the best food for him nor how to go about this. I have a 7 year old siamese cat who is not over weight and I leave hard food down for him and I dont want to punish or neglect coco(my siamese). Alley(the over weight cat) and Coco both get a small bowl of hard food(aprox.2 cups each) every morning at about 3am when my boyfriend leaves for work and that is the only time they get fed. What food is the best to try for alley and how would I feed them without neglecting the other cat

IMO add more wet food and decrease the dry food in his diet.

Feed species appropriate food to both cats and the problem should resolve itself without depriving your other cat. Canned foods with no grains in them or a raw food diet would be best. Please check out this site
http://www.catinfo.org/