Download the .aos file from the Archos website (firmware/operating system)
Select your archos type from the dropdown & save the downloaded file (*.aos) to your desktop - in my case "a404.aos".
Attach your archos to your powered on pc & switch on the archos.
When prompted with "No", "Repair" or "Format", you need to select either format or repair - format is more reliable however removes all data!!! - this allows your pc to see the Archos - do not select done after selecting format or repair.
Open my computer or home you will see your archos present (in my case "F:\a404") - drag & drop the aos file from your desktop to your archos - in this case F:\
Once the file has been transferred to the archos, keep the archos connected by USB & reboot your PC.
The archos will automatically boot up - if frozen at the "Done" screen - reset it with a pin then the archos will boot up.
I formatted the archos drive before dropping the firmware update to it (mine was really screwed).