from another 808

i don't think you can download what you want off the net.(?)
find an 808ex and copy the os onto a zip disk, then load it into your 808.
if the guys at your local shop are friendly ask them to let you have 2 minutes alone with their 808ex demo machine. if not friendly, do it sneakily, i did it was more fun! if they bust you, just say you wanted to try out one of your disks to see if it works on the updated os.
the full info on copying and uploading should be in the hints & tips section.