OK. Here is the section of the /etc/X11/xorg.conf file that you should be editing. If you do not have one, you can create one, customised for your hardware, with the command
That command will also tell you how to test the file, and where to install it if it works.
All of this is in man xorg.conf
Code:
Section "Screen"
......
.....
Subsection "Display"
Depth 24 #Generally. If you are using 16 or 8 bpp, then this is different. It can be ommitted.
Modes "1024x768" "800x600" "640x480"
EndSubSection
EndSection
You simply edit the "Modes" line to include the modes that you want it to use. The system scrolls through this list when you use <ctrl><alt><keypad + or ->.
But, to repeat, this is the wrong way to go about it. You should customize the sizes of fonts and wigits to look as you want. Start with changing the "DisplaySize" entry in the "Monitor" Section. Then go looking in your Desktop Environment for further size settings. You'll thank me for it!