Thank you for contacting us with your question. As a general guideline, if a shrub is spring-blooming, prune it just after bloom, and if it's summer-blooming or later, prune it in spring since flower buds would not have developed yet. Diseased wood can be removed at any time of year. It is best to not remove more than 1/3 of the plant at anytime.  Summer is the worst time to prune in general due to stress to plant, and need for extra care.

If a plant is too large for its space, pruning will not be a permanent solution to keeping it a particular size. Pruning does not stop growth; it actually stimulates new growth. Renewal pruning is for overgrown plants, and takes a few years (depending on how overgrown it is) to get back in shape. It is typically done in the winter (dormant plant) or early spring.  You may loose some of the flowers, but over time it get the plant back in shape with less plant stress. Here is a more information on correct pruning of shrubs from University of Maryland: http://extension.umd.edu/resource/pruning-shrubs-and-hedges-home-garden/