@chrisc leads are normally the issue.
have you actually downloaded the firmware by clicking the listing on the left?
Yes, and on Mac OS nothing happens :(
You also need to erase the existing firmware before writing new firmware.
On Windows 10 I get the little green bar that while it's downloading. On Mac OS this doesn't display. Anyway, it seems to have updated via windows, so I won't bother trying to do it on Mac again.
Thanks for your help.