I wasn't being flippant with the second half of my comment, Mrs Slick knows her onions.
http://www.finegardening.com/pruning-hydrangeas
If you do that you're unlikely to get any flowers this year. If the overall shape of the Bush is congested only cut back about a third of the stems to give the remainder more light and space. Leave the old flower heads on until the frost is over. You will see the new buds forming below the old flower heads.I think I'll cut it back quite hard in the spring, but take some cuttings first.
Thanks folks