There must be more on this topic than any other issue in the forum. Search around and you will find the right thread.
I kicked off with Weather Link software and therefore had to exit the USB mode, to download Cumulus.
I remember that I clicked on the WL program link in my Windows XP PC and a box invited me to switch to 'serial mode'. WL gave me a com port number, which I entered in the Station configuration and hey presto, Cumulus appeared on my screen.
Believe me, if I can do that--anyone can. Took a while, though.
Greetings from London
Follow me on Twitter at @moorparkweather Haven't quite got the hang of reading dozens and dozens of Tweets--never mind finding the time to post my own.