The easiest way I know of is to download the LrnHelper tool.
It is a little difficult to locate unless you have a direct link:
www.usbuirt.com/lrnhelper_0_0_5.zip
Using it you can access the settings for the USB-UIRT including the option to disable the red LED.
I haven't even been able to find any mention of this app on the USB-UIRT page. Kind of wierd but whatever.
You can also access these settings with the plugin for Girder, which seem difficult to locate as well (The settings in Girder that is). I'd tell you how if I could remember. Maybe if I was looking at it.