Instinct 2s will not update software - device memory full

Hi

I'm trying to update the Instinct 2s software via either Connect (iOS) or Express - nothing appears to happen with Connect, but when I try Express I get the message "The latest software does not fit on your device's internal memory".  I've deleted all activities / courses etc. plus rebooted, and hunted through the device folders for anything 'big' that might be stopping this, but nothing - I can't see where all this memory usage is...

Any ideas?

Thanks