SD card / USB method:
a. Format the SD card / USB 2.0 drive (up to 32 GB) in FAT32 mode.
b. Download the firmware and unzip it. (Recommended: WinRAR)
c. Put ALL unzipped files into the root directory of the SD card / USB (no sub-folders).
d. Insert the SD card / USB in the head unit.
e. Power on. Head unit runs the upgrade automatically and restarts when done.
f. Remove and reformat the SD card / USB. (If left in, it will re-upgrade every boot.)
If iPhone connection fails after update: Settings → General → Reset → Reset Network Settings.
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