Internal
You need to be able to unmount your console and be able to flash the internal micro sd card.
On Windows, format your SD card first with this :
https://www.sdcard.org/downloads/formatter_4/
Then use Win32 Disk Imager to flash the firmware.

You can expand the FAT32 partition if you need more space, provided that you used the SD Card alliance formater before on the sd card (Windows only).

Then it's simply a matter (after flashing) of putting everything pack together and power it up.
You may have to press the reset button if it stays black. If it's still black, make sure the internal micro sd card is properly inserted.