Rebooted my Mac mini and that cleared the RAM. (I accidentally double clicked the jar file and nothing happened and thus when I followed the tutorial by Robby, there was already an instance of the server running.)
No need to reboot. You can kill the existing server by navigating to http://<server ip>:51041/kill
Another option is to kill the java process with Activity Monitor.
No need to reboot. You can kill the existing server by navigating to http://<server ip>:51041/kill
Another option is to kill the java process with Activity Monitor.