Hi, welcome to GoY, Pieris are pruning group 8, which usually means a light trim to maintain the shape, immediately after flowering, you can cut out any dead, diseased, or crossing branches at the same time, but they don't usually need pruning, as they don't get any bigger than about 12ft high x 6ft wide, Derek.

I cut ours back quite severely and it bounced back and produced new shoots on what had been bare wood. It seems quite happy to be kept at between four and five feet high and still flowers. Don't do it until frosts have passed though or the new growth might be nipped.