I've had violent thoughts before as well. Everyone has strange thoughts, and they can be scary to some who are genuinely good people and wouldn't hurt anyone. No one has a squeaky-clean psyche and everyone thinks at one time or another things like, "I would really like to take my boss's stupid-looking tie and strangle him with it." You should only worry when you start making actual plans to do these things, like "Tonight, after work, I'm going to dress in the black woolen jogging suit that I bought for this, pull up to my boss's house at 1:05 a.m., and then..." And so on.
Meanwhile, there are many ways to work through these thoughts. First, don't hold them in or they'll get worse. Second, try to find a creative outlet or hobby that can get your mind to process such feelings constructively. Third, try to talk to a professional who is experienced enough to not judge you. I have often told my psychiatrist about my thoughts and he surprised me with how normal a lot of my thoughts really were. Finally, of course, don't act on these thoughts.