hguo83
You can use my method by install on a small sd card / usb batocera 31 pc after on your computer you put the fresh sd with batocera 31 , and your hdd with batocera 30 in another usb port , you delete the file on the windows partition of your hdd batocera 30 and you copy paste the file on sd/usb batocera31 to your batocera 30 hdd
i m sorry im french but here is a tutorial in video
on the video on the left its a fresh usb with batocera 31 , on the right my hard disk with batocera 30 :)
be carefull to choose on windows disconnect / eject usb .