I would also point out that you could just delete it (as root of course). Just be certain to edit lilo.conf and run lilo -t, then lilo.
Deleting the kernels will not remove them from the lilo start screen.
Also, pkgtool will only remove kernel "packages" (.tgz) that you have installed as slackware packages. If you have compiled your own, you will need to delete manually.
As a side note. You don't seem to be running -current, but if you (or anyone else reading this) are, I have found it very helpful to keep all the 2.4.xx and associated packages (alsa, modules, src) installed and install 2.6.xx and associated packages using installpkg rather than upgradepkg, allowing the coexistence of 2.4.xx and 2.6.xx (as opposed to replacement of one over the other) This will prevent the annoying behavior of upgradepkg that "upgrades" the 2.6.xx kernel with the 2.4 kernel when you run a general upgrade of -current from the tree. Even if you never use 2.4, it can reduce these annoyances.
Just to clarify, I use rsync to maintain a local version of -current and upgrade by running a script that essentially runs from /a through /y and upgrades everything that needs it. I could edit the script as well I suppose, but experience has taught me that having two functional kernels listed in lilo can be a very good idea.
I don't use slapt-get or swaret which I think allow some selective upgrade options. I'll keep my feelings regarding these tools to myself.
