Answer: The plants are probably hydrangea macrophylla, or big leaf hydrangea. These plants produce new flowering shoots on old wood. Wait until spring when the leaf buds just begin to swell and then prune. You can cut them back to about 18" above ground level (remove some of the oldest canes in the center of the plant to help renew it, and shorten the remaining canes to about 18"). New growth will emerge from these shortened canes and you'll get flowers on each of the new shoots.
Best wishes with your landscape!
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