How to change uboot setting for boot from?

1. printenv bootcmd
bootcmd=ide reset; ext2load ide 0:1 0x02000000 /uImage; setenv bootargs pm_level=off console=ttyS0,115200 root=/dev/sda1 rw;bootm 0x02000000;

2. setenv bootcmd "ide reset; ext2load ide 1:1 0x2000000 uImage; setenv bootargs console=ttyS0,115200 earlyprintk=ttyS0 root=/dev/sdb1 pm_disable; bootm 0x2000000"

3. saveenv

4. printenv bootcmd   <== check again

ide reset; ext2load ide 1:1 0x2000000 uImage; setenv bootargs console=ttyS0,115200 earlyprintk=ttyS0 root=/dev/sdb1 pm_disable; bootm 0x2000000

Examples:
# setenv ipaddr 192.168.1.50
# setenv serverip 192.168.1.8
# setenv bootargs console=ttyS0,115200 coherent_pool=4m
# setenv bootargs console=ttyS0,115200 earlyprintk=ttyS0
# setenv bootcmd bootm 0xff820000
# setenv ethaddr 00:09:01:02:03:04
# saveenv
# printenv
#
# reset