I'm quite a newbie too, but here's how I'd do it (and have done):
Run terminal. Become root. Run "pkgtool", choose to remove *some* packages. See what packages you want to upgrade from some slackware ftp directory. Example: ftp://ftp.heanet.ie/mirrors/ftp.slac...ackware/gnome/
Let's suggest that you decide to upgrade every package listed in that directory. Upgrading means just uninstalling the pkgs, then downloading the new ones to e.g. /tmp directory, and running "./install-packages". To download, use wget ("wget ftp://ftp.heanet.ie/mirrors/ftp.slac...ckware/gnome/*
" - downloads everything from specified location to the current directory).
Hope this makes sense.