They don't like being moved, especially at this time of year when they're in flower. If it's an old one, to be honest, it isn't worth it. They're not long-lived plants anyway. If you really want to give it a go, then dig out as much of the rootball as you can, and plant it immediately. Make sure the new position is in full sun and is well-drained. You might need to add some horticultural grit to the planting hole to improve the drainage.