I agree with all Chris has said, I've found they do like a change of brand now and then, but if you want to use up the old stuff first, try mixing it into a damp mash in the late afternoon, maybe adding a little bit of mixed corn or sunflower seeds. They will probably go for this and then will have full crops to roost wirh during the long dark nights.
Modern chickens, especially hybrid egglayers, have been bred to do well on layers pellets, which supply all they need in a balanced form. This doesn't mean that it's not necessary to supplement their diet with a bit of variety, epecially green food and short grass, and roaming the garden is excellent for this. But its a mistake to indulge them with lots of human food as 'treats' which will make them fat and not want to eat their pellets. Too much corn will also unbalance their diet - the suggested maximum amount, for treats and catching them, is one small eggcupful of mixed corn per hen per day. If you measure that out, it's not a lot, and you can actually treat and train them with even less than this.