Download the latest Edison image and unzip
Download dfu-util from dfu-util Homepage. choose win32 version if you are using Windows
Copy dfu-util files to the same folder that you unzip Edison image to.
Unplug both usb cables
Plug both usb cables and wait
Check your serial terminal and most likely the board should boot with refreshed firmware
I tryied it, but I got the message:
Device has DFU interface, but has no DFU functional descriptor.
Cannot open DFU device 8087:0a99
I reinstalled Edison drivers (iotdk_win_installer.exe) and now I could see Edison as a drive. Then I copied the image files and run "reboot ota" and the new image was installed.