I don’t know why your software or OS can not be updated.
According to the official instructions (github.com/mcguirepr89/…/Installation-Guide) is should just be a normal raspbian. Nothing on there says it needs a legacy version, but I may be overlooking something.
If you installed it some other way or did it long ago then maybe do the setup over again from scratch with the newest raspbian version? (Don’t forget to backup any data you’d want to keep)