There are a few way to update the firmware but for the moment as I am not writing any code I have chosen to use an executable containing the most recent firmware. I should note the little executable program's UI is in Chinese and a bit difficult to work out but as there's only one button it's not impossible...

After updating to 902, you can no longer use Putty to issue AT commands as it doesn't send CR+LF so I have changed terminals to Termite version 3.1 and it works a treat....