Do you need to? I've had three of these for 2 years now and they've hardly grown at all.
How big is your plant now Tatumjm and how big was it when you planted it?

If you need to reduce the height, or there are stems poking out where they shouldn't, simply cut the tallest or unruliest stems out at the base in early spring. New stems will shortly grow to replace them. I wouldn't remove more than a quarter of the foliage at a time. They will survive shearing, but they never look right again. As Beattie says, though, they can happily go decades without any pruning.