Many bloom on "old wood", so should not be cut back. You have to know the hybrid and read the care guides. If you don't know the hybrid, wait until it starts to leaf out, then just prune off the obvious dead stuff , cutting above the first live leaf bud. If it's an old plant, check the large branches in the middle of the plant - tug gently and pull out any loose ones- I had a big old hydrangea that would "self prune" that way.
If you must cut the whole plant back, just realize you may go a year without blooms.
We cut ours back each year, and we have the Dear Dolores variety. Here are some instructions: https://thekitchengarten.com/why-and-how-to-prune-hydrangeas/
Totally depends on variety of hydrangea. Click here to read the post I wrote on pruning peegee hydrangeas
Cindy, are the flowers round shaped or more conical shaped? Like I tried to explain in that priming link I gave you above, if conical then they're pee gee and will bloom on fresh wood, new growth. That means you can prune in the spring without fear of cutting off the flower buds formed on old growth.