Enjoy Slackware 15.0!
The simplest way is to boot the system with the Slackware install media as described at the first screen:
boot: hugesmp.s root=/dev/sda2 ro rdinit=
where /dev/sda2 is your root partition. Than you can make initrd if needed, edit /etc/lilo.conf if needed, and fix bootloader with:
# lilo
— Serg Bormant 2017/04/22 18:12 (UTC)