I just did this upgrade. All you need is the openwrt-brcm-2.4-squashfs.trx file. I am not sure what the .trx2 file is.
You can use these commands to perform the upgrade directly on your device:
# cd /tmp
# wget http://backfire.openwrt.org/10.03/brcm-2.4/openwrt-brcm-2.4-squashfs.trx
# mtd -r write openwrt-brcm-2.4-squashfs.trx linux
This upgrade will absolutely erase your config, so you should back up any configurations or settings that you don't want to lose, or be prepared to recreate them. Your device will go back to "firstboot" settings, where it uses IP 192.168.1.1, and you must telnet to that IP and set your password to enable SSH, then start configuring from scratch.