You may use varios operating system to update the firmware for SmartLink.
Get USB Boot utility (done only once)
First of all, you will need USB boot utility which will force system transition to bootloader state.
Download USBBoot tool here: USBBootTool
Forcing bootloader and image flashing
Once you have the boot tool, let's start it and flash the firmware.
Open command line and locate USBBoot
Start bootloader tool
Connect USB cable, turn on power supply (make sure to connect USB cable before providing power)
df -hto find out the mounting point of the unit (look for 3.9GB unit since eMMC of SmartLink has this amount of flash memory)
Locate the firmware file
To flash image from file (make sure to set correct filename and sdX):
gunzip --stdout IMAGE_NAME.img.gz | sudo dd bs=4M of=/dev/sdX status=progress
Upload process may take up to 15 minutes. Progress will be displayed on the screen.