Haven't tried it with a HX product, but it works with the POD Go -
Download the latest version of L6 Updater & HX Edit, and any version, other than the latest, of the firmware.
Boot the HX in to 'update mode' - hold down the 'Page >' button while switching on.
Plug in to you computer and start L6 Updater in 'offline mode'.
Manually install the firmware you downloaded.
When it's done, close Updater, reboot the HX Stomp, do a factory reset.
Start HX Edit and follow the instructions, to the letter, to update to the latest firmware.
Like I said, works on the POD Go, haven't tried it on my Helix, but I don't see any reason why it wouldn't work.