It's usually recommended to do it gradually over a couple of weeks so they don't get an upset stomach with the change. So you could start by mixing a quarter Harry Hamster with three quarters of the current food for a few days. Then a third HH and by the second week, half and half - then a few days later mostly HH then by the end of the second week all HH
Thank you! He seems to be quite selective with his food, the larger pieces are going untouched at the moment - it’s the sunflower seeds as usual which are first to go!