So if you are on OpenWRT firmware and you will go back the original Firmware from the manufacturer you need to modify the original firmware because the original firmware you can't flash with OpenORT running.
- So go and download the original firmware
- Use dd and cut the first 131584 byte, or in HEX 0x20200
- dd if=original_firmware.bin of=openwrt_flashable.bin skip=257 bs=512
- If you have serial access you can flash this image at the U-Boot prompt and be able to use a tftp server for the flash process
- setenv ipaddr 192.168.1.1
- setenv serverip 192.168.1.4
- tftpboot 0x80060000 openwrt_flashable.bin
- erase 0x9f020000 +0x7c0000
- cp.b 0x80060000 0x9f020000 0x7c0000
- boot.m 0x9f020000
- If you don't be able to flash via the serial console you may be flash with normal OpenWRT flashing method the converted firmware
If everything is done, you should reboot the router and you can login via the original IP: 192.168.0.1
I hope this helps a little bit and good luck!
More Information you can find here at the OpenWRT forum