[Iridium]

eXeCuTe,
1st.
What is the purpose of changing your firmware ?
2nd
There is no way to know for sure the correct firmware until you disassemble unit and report the board id number. Players may look the same (same button configuration, etc.) and have completely different FW inside because the pc board inside is different.

ALWAYS BACK UP YOUR FW... 1ST!

Also, the CD that came w/ unit may have correct FW on it. Look for.bin file.
If you simply want to change background pics, follow the guides on this site for fw mods (themes).

Iridium