In the game options, I found the place to change the resolution away from the super low 1024x768. I am using a laptop with a Radeon 6770m with a native resolution of 1366 x 768. The option is there, however when I try to click on it nothing happens. I also tried selecting with the keyboard, but pressing enter on it also does nothing.

There is a prefs.prop file in the Telltale Games directory under My Documents, however it is not a plain text file. I found other people that had a similar problem with the demo on the official forums, however the only answer the developers had was that they were never able to reproduce it but they issued a patch. I have the latest updated GOG version.