Questions about adjusting screen resolution by redhat

For details about how to adjust the screen resolution of redhat-Linux general technology-Linux technology and application, see the following. I checked the redhat on the Internet to adjust the screen resolution. Many of them refer to modifying/etc/X11/xorg. the "Monitor" item in the conf file, but the root of my file does not have this item. below is the content in my file:
Section "ServerLayout"
Identifier "single head configuration"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Synaptics" "CorePointer"
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
EndSection

Section "InputDevice"
Identifier "Synaptics"
Driver "synaptics"
Option "Device" "/dev/input/mice"
Option "Protocol" "auto-dev"
Option "Emulate3Buttons" "yes"
EndSection

Section "Device"
Identifier "Videocard0"
Driver "vesa"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Videocard0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
EndSubSection
EndSection

How can I modify the screen resolution ??