It's usual to cut down to 2 meals at about 6 months & I would then keep to 2 meals a day even when your pup is fully mature, although some owners do cut down to one main meal a day at about 12 months old. There is no need to change the diet radically - if your puppy is happy eating a complete food (kibble), then he can continue to have this as he gets older, although you should change over to the adult formula (assuming he is eating puppy formula now) when he is fully grown (usually at about 8-9 months old).