Answer: You can use shears or you can snap off the spent flowers. If you look very closely at the stem where the flower emerges you should be able to see two tiny buds opposite of each other on the stem at the base of the spent flower. This is the point of growth of next year's floral display so you'll want to be careful when cutting or snapping the old flowers off so you don't damage the immature buds. As for keeping your shrub compact, you can shear the rest of the shrub or simply pinch out the very tips of each of the remaining (non-flowering) stems. When you pinch out a newly forming leaf at the tip of a branch it should result in two new stems at the point of pinching or shearing. If you're still not sure, try pinching just one or two branch tips and watching them over the next few months. I think you'll find the mystery of pinching and pruning solved when you observe the growth pattern.
Hope this clarifies things for you!
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