You will want to edit the file /etc/lilo.conf, the easiest way is probably just to press ctrl+F2 (to run a command) and enter "sudo kate /etc/lilo.conf" which will open the file in the kate text editor (the sudo bit means you'll have permission to save the file). Then when you have made saved your changes do Ctrl+F2 again and this time run "sudo lilo" which will update lilo to use the new config. Hope that helps.