How did the new media (things like films, literature, and music) of the 1920s affect Americans' values?
First of all, it is a little bit dangerous to say for certain that the media changed values. If the media change and the values change, the media may have caused the values to change. However, the change in values might also have caused the change in media. Alternatively, it might have been some third factor (a change in technology, for example) that caused both changes.
That said, you could certainly argue that the new media eroded the old values and helped to bring in a new set of values. You could argue that the movies (this was before widespread censorship and there were some pretty racy things allowed) and music (jazz, most notably) encouraged people to take on more hedonistic values. The "wildness" of jazz music and of dances like the Charleston can be said to have brought around changes in dress and behavior such as those exhibited by the flappers.
There was clearly a change in values in the '20s with old values falling away to some extent. At the same time, there were new kinds of media. You can argue (though you should be careful about doing so) that the new media helped cause the change in values.