How to change the resolution of Screen?

I am using 4.3" display attached with Colibri_T20 Evaluation board which requires 480x272 resolution but the Kernel has default 640x480 resolution.
I have tried ‘xrandr’ command.
So how to change the resolution from 640x480 to 480x272.

Please have a look at the following article on our developer website.

I am trying to use global environment variable “setenv” from command line to set the resolution but kernerl does not have this command.

Those are U-Boot commands. To issue them from within Linux user space you would need to use the fw_printenv/setenv commands as e.g. indicated further down: http://developer.toradex.com/knowledge-base/framebuffer-(linux)#24-bpp