How does one unbind a port?

Managers,

My apologies in advance if this turns out to be a RTFM
kind of questions, but I am in a jam here. I get the 
following message when trying to start a process that 
uses port 5600:

 java.net.BindException: Address already in use: Unable to bind
 port number 5600 

This suggests that some other process is using that port, so my
question is:

How do I find out what process (pid) is using the port so I can
kill it? Been trying things with netstat, but can't find the pid.

Ron Babcock, Dir. Admin. Computing
Casper College
Casper, WY 82601