First you must have installed rocket loader from the control panel > game mods.
If necessary change the rcon password Rocket.config.xml by editing the file from the control panel > config files . Also note the rcon port number specified in this file. Save and restart the server.
Now download the rcon utility HERE
If you are having issues with the cron utility simply download Putty
Run (double click) the executable file and enter the server address ( without port ) and the RCON port of your server in the window that will open and click "Connect."
If you are using putty enter the server IP and the server rcon port and select the "telnet" protocol.
Once connected type:
login your_rcon_password
and validate.
You can now send administrative commands such as:
kick player_name
Night
Day
etc.