Clean out old kernels

[NoOp]

I've seen it before, googled for it, but just can't find it tonight...
What is the easiest & safest way to clean out old kernels?

On one of my systems that I've just upgraded to Gutsy my grub menu looks
like an archive of Ubuntu kernels. I know that I can just edit those out
from menu.lst, but I'd also like to safely remove the old unused kernels
as well. The grub list looks like this:

2.6.22.-12-386
2.6.22.-12-386 recovery mode
2.6.22.-12-generic
2.6.22.-12-generic recovery mode
2.6.20-16-386
2.6.20-16-386 recovery mode
2.6.20-16-386-generic
2.6.20-16-386-generic  recovery mode
2.6.20-15-386-generic
2.6.20-15-386-generic recovery mode

Suggestions/recommendations on what to keep and what to remove?