Won't affect the plants in any way. Use sharp cutters and remove the spent blooms and their stems just above the last bud on the cane. That portion will be dead.
Rb

... or better wait untill buds starts swelling and you'll clearly see where to make a cut.

I have an Endless Summer Hydrangea that seems to be mostly dead, except for a few branches. By last fall, the majority of the branches were brown with no growth or green leaves. It is about 3 ft high and wide. There are about 3 branches that were green and were producing blooms. Needless to say, it was a very sorry looking Hydrangea.

It is a 4 year old plant, that was originally in a location with too much sun. Early last spring, I moved it so that I wouldn't receive the southern exposure sun it was getting, but rather 3 hours of morning sun and rest of the day shade.

It is now close to Spring and I still don't see any growth or progress on this shrub.

If, in a few weeks, I don't see any green growth on those dead/brown branches, shall I dig up and toss the whole plant? Could I divide the root ball so that the portion or side of the shrub that had life could possibly survive and grow into a larger shrub?

Thanks!
Tulipsmiles

tulipsmiles, my recommendation would be only to remove or cut back to the base those stems that show no signs of life or new growth. Often that is enough to encourage additional shooting from the root crown. Mulching with compost or fertilizing appropriately might also help to encourage new growth. In general, unlike perennials, woody shrubs such as hydrangeas do not respond well to division - you risk damaging the rootball and killing the plant.

FWIW, there have been countless posts here about folks having difficulty or getting poor performance with 'Endless Summer'. If this plant does not respond well this season and put out some nice vigorous new growth, you might want to consider replacing it with a more reliable selection.

Thanks Gardengal - your feedback is very much appreciated. I will cut out those dead stems and hope the energy is diverted to new growth.
Thanks!