Use the Comcast remote and press MENU button twice. Scroll down to the Favorites and select. Press the right arrow to go into the channels marked as favorites. Scroll until you find the channel you want to remove and press the OK/Select button.
I know that with my SA box I can also use the first menu screen and scroll down. There is a spot on my first menu for adding or removing a channel from favorites. But that is probably not the same from the sound of it with the HD RNG110. Didn't see much in the manual for setting favorites either.
But I included a link for the set top box page which also has the links for the online manuals.
Thanks commanguy. One thing to mention though is that you have to select SETUP in the first screen in order to get to the Favorites. Then it is a drag to get to the channel you want, but when you do it works.