[CentOS] Safe method to remove old kernels

# rpm -qa | grep kernel-2 | sort
kernel-2.6.9-42.0.10.EL
kernel-2.6.9-42.0.2.EL
kernel-2.6.9-42.0.3.EL
kernel-2.6.9-42.0.8.EL
kernel-2.6.9-42.EL
kernel-2.6.9-55.0.2.EL
kernel-2.6.9-55.0.6.EL
kernel-2.6.9-55.0.9.EL
kernel-2.6.9-55.EL

I'm running the most recent kernel available, and I've never had a
problem with any past kernels, so I don't believe there's any reason
to keep all of them.  I guess kernels get a fresh install instead of
an upgrade?  Can I safely rpm-e the old kernel packages?  Should this
be something I do through yum instead?

Some of my CentOS servers have even more old kernels than this sample.

Thanks,
Scott