How do you have records expunged?

About six years ago I was charged with a crime I did not commit. Later the charges were dropped because the prosecutor realized there was no way for him to make his case. Even though I was never convicted, the charges still appear on my record. I have never been in legal trouble any other time. I am fairly certain that I did not get a job that I applied for, because of this record. I would like to have these records expunged, but have no idea where to start. Please help.