Help Needed! Need to switch foods any help would be appreciated

[theparrisfive]

thats what tank was on too and he just acted like he was starving and was losing so the vet said to up him and he was still losing. hes shedding horribly i dont know how he is bald honestly. weve also noticed he gets "hairballs" after eating and he has pimples on his face so its pretty well time for a food change.