If cats become used to being fed too much food, it can be difficult for them to get used to a restricted amount of feeding. Cats enjoy the act of eating, just like humans, and so you need to find ways to give them enjoyment in different forms, such as getting new toys to play with, or simply by engaging with them more as their carer.
Over time, most cats learn to adapt to the new way of feeding, and they become less hungry. If your cat does continue to seem hungry all the time, you should take them to your DVM veterinarian for a health check in case there is an underlying health reason for this (such as hyperthyroidism). If it turns out that your cat is in full health, but simply very hungry despite being fed the correct amount of food, your veterinarian may be able to suggest a type of high quality cat food that is more likely to make your cat feed full (satiated).