Step 1: Log into your game control panel.
Step 2: Open the "File Manager" and right-click delete the "steamapps" folder if it is present.
Step 3: Run the "Update Server Files" icon.
Step 4: Open the serverconfigmain.xml file in the Configuration Editor and save. Be sure to adjust settings to your liking!
Step 5: Restart the server.
You should be all set! If necessary, you can reinstall the server by clicking the "...More" button -> Reinstall.