1) Prepare a USB stick, format FAT32. I'd recommend using this HP Format tool.
2) Download the image you would like to use, extract the venton-hdx folder.
3) Copy the venton-hdx folder to root of your USB stick.
4) Connect to a REAR USB PORT on your Venton Unibox HDx.
5) Power on and wait for the flashing process to automatically flash, once complete you will see a complete message on front VFD. DO NOT POWER OFF DURING THE FLASHING PROCESS!

Once you copy the venton-hdx folder to USB stick as in step 3, you should see the venton-hdx folder when accessing the root of the USB stick. Folder structure should be venton-hdx > flash files.

I'd also recommend installing Teracopy, although not essential, to your PC to copy files from PC to USB stick, less chance of corrupting flash files.