You should follow the advice and "wipe config during upgrade".
So, unselect the "Keep settings"...
The backup will brick you if you restore it to the new firmware.
The old network config (/etc/config/network) is not compatible with the new DSA switch config.
Usually all other config files are compatible.
("system" may have a wrong LED config, but does not brick you.)
You might also read this for a quick & dirty approach...