The firmware of a R4 is fixed and cannot be changed. If yours can be changed then it's not a R4 but a R4 fake.
If it is a real R4 and it still doesn't work then format the SD card with the panasonic formatter, then put the _rpg folder on the card, then _DS_MENU.DAT and then the .nds files. The card should boot fine (if it is a real R4).
If it's not a real R4 then you have to find another kernel since Wood R4 does not work or by a new full clone R4 which is technically identical to the original R4.