A Diagnostics.Process question

Hello.

I'm simply making a media player. You execute the program with a filename as an argument and it runs it. Now, if the user runs another instance of the program, I want the previous instance to receive the new filename from the new process.

You execute some song Song1.mp3 and it plays. Now you execute Song2.mp3, I want the player to change to Song2.

Now, I used Diagnostics.Process to get a previous instance and I have the handle of that process and all, but what should I do?

What I can do is to close/kill the older process, and resume the new process, but that leads to some problems:
I have to take care of the array of processes and find out which one ran first and all that, and it will also cause a bad termination of the older process.

Any ideas?
I hope you know what I'm talking about.