So the used space on the USB if no files are showing is the space allocated to the formating of the drive. You should not need to re-download the software, that should be on your PC, when I do file moves on the computer to a USB I typically have two small side by side windows open so I can see the file on the I want to move, then I have the target location (USB) also open so I can drag and drop the file I want and not be switching between window panels. (likely a run on sentence and hope it makes sense)
Once you see the file on the USB, you should be able to disconnect the USB and connect it to the bike, and that should trigger the the update once you have the bike set to Acc.
If the file is dropping the .ISO on the USB side that is a mystery to me. When I checked my USB for the file I used it was labeled swdl.iso.