If you are letting the canned food sit out all day, then its too long to be left. Try putting out some dry kitten food (Royal Canin Baby Cat would be good). And offer the canned food 3 or 4 times a day - maybe about 2-3 teaspoons at a time. Kittens can't eat a lot at a time.
If the kitten is only 4-8 weeks old, it still should be nursing from mom. They are not weaned till 8-10 weeks old and don't eat very much solid food till 6-8 weeks old. How old is this kitten? There is a BIG difference between a one month old kitten and a two month old kitten