When I’m testing a new process, I like to use the Process Overview report to look at various aspects of my test cases.  But I don’t like it getting cluttered with dozens of completed test cases.  I like to delete my process instances from previous rounds of testing.
How can I delete process instances after they have already completed?  I can’t.  What I do is prevent my process instances from completing.  At the end of the process where it would normally end I add one last server code event and make it asynchronous.  This forces the event to wait forever for some outside action. 

public void Main(Project_0c5d… K2)
{
    K2.Synchronous = false;
}

Then when I want to get rid of the previous round of test cases, I go to the management console and delete them all.  Be sure to check “Delete Log Entries” in the delete dialog.