You need to run the lilo version included in Slackware 14 as it can handle bigger kernels, as the ones included in Slackware 14. The lilo version in 13.37 can't do that.
There is
another thread about that. « Même faute, même punition ».
Besides that, read carefully UPGRADE.TXT at the root of the Slackware 14 distribution media and
this How To on SlakDocs.