How does CentOS Delete unnecessary startup items after kernel upgrade?

How does CentOS Delete unnecessary startup items after kernel upgrade?

1. # uname-a view the current kernel version

Linux localhost. localdomain 2.6.32-358.23.2.el6.i686 #1 SMP Wed Oct 16 17:21:31 UTC 2013 i686 i686 i386 GNU/Linux

2. # rpm-qa | grep kernel: Find the version number to be deleted

Kernel-firmware-2.6.32-358.23.2.el6.noarch
Abrt-addon-kerneloops-2.0.8-16.el6.centos.1.i686
Kernel-devel-2.6.32-358.el6.i686
Dracut-kernel-004-303.el6.noarch
Kernel-2.6.32-358.23.2.el6.i686
Kernel-devel-2.6.32-358.23.2.el6.i686
Kernel-2.6.32-358.el6.i686
Kernel-headers-2.6.32-358.23.2.el6.i686
Libreport-plugin-kerneloops-2.0.9-15.el6.centos.1.i686
The above is the kernel version number on my computer, where red indicates the version number to be deleted

# Yum remove kernel-devel-2.6.32-358.el6.i686
# Yum remove kernel-2.6.32-358.el6.i686
4. Check grub. conf and find that the excess startup items have been deleted.