See if this makes any sense to you → Is more storage better? - #7 by F150Chief
Not sure exactly what you mean by serial port, as said before, if you have a picture just send it.
Also, why are you doing this exactly?, trying to convert the unit to NAV?.
About upgrading without any image, I can’t answer for that.
I mean sure, if everything goes ok then yes, you can upgrade it as you would to a normal unit leaving it unattended. But how would you know if everything is ok?. Any issues during the process and you won’t be able to see what’s going on, that’s not safe in my book, since you would be blind.