Unfortunately, Gazanias in the UK are only annual plants, usually planted as summer bedding, so they'll die come autumn/winter. That means dividing them now isn't a great idea because you'll disturb the root system and they won't flower for a while, so its not usually something people do, but you can give it a go if you think you have to, or just remove a couple to give the remainder more room, filling the gap with more potting soil.