Is Update from 7.3 to 8.0 really possible?

I tried to update my 7.3 configuration to 8.0 using boot.iso. Strangely, the base-package is not updated no matter what I do. The box for that selection is stuck at "no", and is not modified. Has anyone successfully updated to 8.0 by using one of the mirror sites, or by downloading the whole package to her/his local place? This is my first time that I failed in doing so. Regards, Hugh