Unfortunately Slackware 12.0 does not unable update of OS by default, slackpkg needs to be installed from the install CD/DVD which is located in “extra\slackpkg” folder.
installpkg slackpkg*.tgz
uncomment only one mirror on /etc/slackpkg/mirrors file which represent your version.
slackpkg update; slackpkg upgrade-all
the above command will upgrade your machine.
