How to set display resolution manually?

[houkensjtu <houkensjtu@gmail.com>]

Hi debianer!
I installed debian-wheezy on my lenovo x121e laptop, and since it comes with a only 11.6 inch display, I plugged in a monitor through VGA port.
Fortunately without any configuration I could got the same content display on both my laptop and the monitor I plugged. However the resolution are both 1366x768, which is not enough for my full HD monitor.

So I don't want fancy dual-display, I just want to fix the resolution on my monitor to become 1920x1080. How can I do it?

(I read several articles said about xorg.conf, and I re-write piece of my xorg.conf:
Section "Screen"
        Identifier "Screen0"
        Device     "Card0"
        Monitor    "Monitor0"
        SubSection "Display"
                Viewport   0 0
                Depth     1
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     4
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     8
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     15
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     16
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes     "1920x1080"
        EndSubSection
EndSection

Then I restart x by "startx", what I got is a zoomed region which I guess is 1366x768 inside the monitor, and the left region is black.)

Please help!