The time to prune Pieris is after flowering so now is a good time to trim it to the shape you want.

If you want to cut it back drastically I would do half at a time. It can regenerate from quite low down on the old branches, but will need lots of its existing leaves to be going on with, until it makes new growth to replace what you cut off.

Thanks you for your replys I will prune it a little bit.