If you must change foods, introduce the new kind a small amount at a time mixed with what its been use to. Cats can be finicky eaters but you can wean them away from the other food. Most cat foods provide a complete and balanced nutrition. You should vary the menu. Cats eat to satisfy their energy needs.
Dry foods have more energy making elements than semi-moist or moist foods.
Dry food should be left out for the cat if you work. One of the other two types should be fed to the cat once a day. Feed it as much as it can eat in twenty minutes. After the cat leaves the bowl remove it and throw the remaining food away. Kittens should be fed three times a day until they are six months old.