How can I change x-loader resolution?

I want to change resolution dvimode=1024x768MR-16@60 to 848x480@60.
How can I change it? Thank you for your helps.

Selim

Texas Instruments X-Loader 1.4.2 (Feb 19 2009 - 12:01:24)
Reading boot sector
Loading u-boot.bin from mmc

U-Boot 2009.06-rc2-00003-gc06326c (May 19 2009 - 15:14:43)

OMAP3530-GP ES3.0, CPU-OPP2 L3-165MHz
OMAP3 Beagle board + LPDDR/NAND
DRAM: 256 MB
NAND: 256 MiB
In: serial
Out: serial
Err: serial
Board revision C
Die ID #17420003000000000403230910015017
Hit any key to stop autoboot: 0
OMAP3 beagleboard.org # printenv
bootdelay=10
baudrate=115200
loadaddr=0x82000000
console=ttyS2,115200n8
vram=12M
dvimode=1024x768MR-16@60
defaultdisplay=dvi
loadbootscript=fatload mmc 0 ${loadaddr} boot.scr
bootscript=echo Running bootscript from mmc ...; source ${loadaddr}
loaduimage=fatload mmc 0 ${loadaddr} uImage
mmcboot=echo Booting from mmc ...; run mmcargs; bootm ${loadaddr}
nandboot=echo Booting from nand ...; run nandargs; nand read $
{loadaddr} 280000
400000; bootm ${loadaddr}
dieid#=17420003000000000403230910015017
mtdids=nand0=nand
mmcargs=setenv bootargs console=ttyS2,115200n8 root=/dev/mmcblk0p2 rw
rootfstype
=ext3 rootwait omapfb.video.mode=640x480MR-16@50
serial=17420003000000000403230910015017
bootargs=console=ttyS2,115200n8 noinitrd root=/dev/mmcblk0p2 video=
omapfb.mode=
dvi:848x480@60 init=/init rootfstype=ext3 rw rootdelay=1 nohz=off
androidboot.co
nsole=ttyS2
bootcmd=mmc init;fatload mmc 0 80000000 uImage;bootm 80000000
nandargs=console=ttyS2,115200n8 noinitrd root=/dev/mmcblk0p2
video=omapfb.mode=d
vi:1280x720MR-24@50 init=/init rootfstype=ext3 rw rootdelay=1 nohz=off
androidbo
ot.console=ttyS2
stdin=serial
stdout=serial
stderr=serial

Environment size: 1138/131068 bytes
OMAP3 beagleboard.org #

this is not done through X-Loader but U-Boot:

setenv dvimode=.....

Actually, I want to change resolution when sdcard is unplugged. is
there any suggestion?

Thanks,
Selim.