Change monitor refresh rate in Ubuntu

If you have a non-standard setup you might be forced to do some manual
configuration. Edit /etc/X11/xorg.conf to do that.

What you want to change is the HorizSync and VertRefresh values in the
Monitor section. Here is an example from setup.

Section "Monitor"
      Identifier   "SyncMaster 975p"
      VendorName   "SAMSUNG"
      ModelName    "SyncMaster 975p"
      HorizSync    30-96 <===============        VertRefresh  50-160 <===============        DisplaySize  361 271        Option       "DPMS" EndSection