I found these instructions on the xtrend website

1. Download the attached zip file.

2. Unzip and copy + paste the et8000 folder on to your USB Stick

3. Insert USB Stick to your ET8000.

4. When you see the message "Flash Image?" on your front display, press the CH 'down' key (instead of the 'up' key which you would normally use to flash an image).

Is this correct? I always press OK when it asks for flash