Update from 7.1 to 8.0

Hello I am trying to update, via FTP, from 7.1 to 8.0. I use the boot CD, and am able to download all the packages. However, when the system gets past the red warning screen, it reports an error and then crashes. On restarting the system, it welcome screen is still that for SuSE 7.1. Can anyone help? Thanks, John.