Just nip off the head and leave the leaves to turn brown and eventually they will disappear. Don't tie them up. I know it might look untidy but it's only for a while. When you take the heads off, the nutrients go back down into the bulb and will assure a good plant next year. Ditto with tulips but you can pull those up and dry them by hanging in a net (some old tights or knee highs) from the shed or garage ceiling. Next year you then have bulbs ready to plant in early spring.