I use imgburn (
The Official ImgBurn Website).
Skip if you have your own burner.
Download and unzip, install imgburn, then v32 image and then open imgburn, and select the "write image file to disc" then select the modded.iso(i think) file.
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Select the write speed as x1 (or the slowest rated speed for the disc, you must do this) and then burn on a good quality cd.
When its finished writing your new firmware cd,
Go to the car open the drivers door,
Go to the nav computer and press eject on drive,
Eject the map disc,
Switch ign to pos 1, leave door open.
Insert firmware disc into drive, follow instruction on nav screen.
Wait (approx 6 mins) till sat nav asks to eject cd and reboot.
Eject cd,
Confirm reboot.
That's it.
Do not switch off ignition or close the door when doing the upgrade.