British Columbia: Pruning & Trimming Lacetop Hydrangea

Two years ago, I "inherited" a lacehead hydrangea when my husband and I moved to our residence in Steveston (southwestern Richmond). It was probably already somewhat overgrown when we moved in. Since we've lived here, the hydrangea has grown approximately 1-1/2 feet taller.

I would like to reduce that height as it is over 5 feet tall and blocking a window.

I'm a noob with gardening and haven't a clue how to go about pruning a hydrangea without damaging it. Do I cut stems at an angle? Can I cut down to the older wood, or must I limit pruning to the green stems? When is the best time of year to prune it?

Help would be greatly appeciated.