There is really no need to do anything as the plant's flowers are in late seasonal color. If desired the completely faded dried florals can be removed or kept for winter interest. Cut just below the flower and above the next set of leaves. As the plant gets larger in the warm growth season you could prune occasionally to shape it. First, remove any dead or sickly branches.  Remove old dead branches just above live nodes. Do this every year as needed.  Prune the remaining branches slightly to shape the plant. 

You can find more information in our guide Hydrangea How-to's.

Courtesy of NYBG Plant Information