I have two spireas – Little Princess and Goldenmound. I believe both are considered summer blooming variety. Do the flowers need removed as they die? If not, when. Also have a White Out Hydrangea. Same question.
Pruning the spirea right after blooming is a good idea and keeps the garden looking tidy.
Your White Out Hydrangea should have all dead wood removed in the spring.
Then every 5 years prune out 1/3 old wood to the ground each spring to rejuvenate your plant.
Dead head old blossoms to encourage more blooms throughout it's growing season.
Here are a couple of links.