To begin with, this guide is only for Unturned Rocket servers. There is no functionality for RCon in the base Unturned game.
To enable remote access for your server, you will need to enable the setting under thefile on Clanforge. This can be completed by changing the following line:
Once this has been enabled, you will be able to login using Telnet by connecting to your Game IP using the Admin Port, (This can be found on your Server page in Clanforge) and using your random Admin password which can be found under your Profiles Settings tab.
You can then proceed to run console commands as normal.