You either take the case yourself, which I have done; this should be quite straightforward considering the promisary note, or get a solicitor to represent you.
If you choose to take the case yourself, go to the court, they will give you the necessary papers and tell you your next step. It is all quite simple. Then you will just wait until you hear from the court with a date to attend.

Take him to court.
The first step in the United States is to compare the amount of the promissory note with the limits for small claims in your state. If you can go to that court, you do not need a lawyer. Cases are easy to file.
If the amount is too large, you should hire a lawyer because while you can get a judgment, you still may not get any money and you will need to file more actions to collect.