I have cut mine back really hard in the past and they just grow back. It depends what you want to achieve, if you dont mind losing some height you could cut all back by half cutting just above a bud, but if you want to maintain some height just cut a third of the branches at the base. New shoots will come from where you have cut. Do it now before it starts into growth or after flowering.
There such an amazing flower. All the detail and colors. Their one of my favorites. Just to hot for them but I do get do enjoy them in spring until it gets just to hot for them. This year I'm going to bring them inside that'll b great if it works. But yes are gorgeous