I know, I know... they are blooming... but you must do it. You must give them a little off the top and give them some organic fertilizer while you are there.
The only reason not to is if you have an arching variety or a climber. Then you will only take out anything dead. Excellenz von Schubert in the blue pot.
Just take your pruners and go all the way around. Go ahead, you can do it. Stand back and watch the blooms you will see next month.