I was momentarily hopeful when I found this thread for 1.03B, but unfortunately, my camera doesn't even give me the option to upgrade the firmware.
You don't need to change or upgrade the firmware on your camera. If you have a camera with 1.03B firmware installed, use the 1.03B beta version of CHDK for the IXUS120-SD940
You won't be able to find the upgrade firmware option because the PS.FI2 file is not present in the zip archive for 1.03b beta port. You have to make your <4GB SD card bootable, and the easiest way is to use cardtricks.
Actually, you cannot upgrade or change the firmware on your IXUS120-S940 at all. Canon does not provide support for this and CHDK does not change the firmware on the cameras it operates on.
You also cannot use the "upgrade firmware" method for activating CHDK. Only the bootable SD card with the Lock switch in the "On' position is currently support for activating CHDK on the IXUS120-SD940. The PS.FI2 file needed for "upgrade firmware" booting is not available for the IXUS120-SD940.