I tried this using 8.1. Screen Resolution is in the
"System-Preference" area. I couldn't find anything that had to do with
selecting a monitor. Couldn't find anything like "Screens and
Graphics" either. Displayed resolution included 1680x1050 which is
what I am using, but I wanted to try your solution.

Changed it to 1400x1050. It changed ok, but looked awful. Tried to
change back to 1680x1050, and it wouldn't change. Had to restart. It
came back as original - 1680x1050.