Regarding which version the phone should be upgraded, you can distinguish it by the follow way.
Due to the distinction of the hardware platform of the phone, if the DSP parameter of the phone with "M", then
UC902/UC903/UC912(G)(E) need to upgrade the fw900M.rom
UC923/UC924(E)/UC926(E) nned to upgrade the fw920M.rom
If the DSP parameter of the phone without "M", then
UC902 upgrade the fw902.rom, UC903 upgrade the fw903.rom, UC912(G) upgrade the fw912.rom
UC923 upgrade the fw923.rom, UC924 upgrade the fw924.rom, UC926 upgrade the fw926.rom.