"I have some old version kernels to removed(installed them through packages both kernel-source and kernel)."
Issue the command:
which will tell you the name of the kernel that you are running on. Then go into /boot and delete every kernel other that the one you are running on.
Each kernel has a directory in /lib/modules containing the loadable kernel modules. There will be a directory called /lib/modules/your-kernel-name. That is part of the kernel that you are running on. You can delete every other directory in /lib/modules.
You also have initrd and System.map files in /boot. Some of these may belong to the kernels that you are deleting. If so then delete the initrd and System.map files that correspond to the kernels that you delete, but of course retain the initrd and System.map that belong to the kernel that you are running on.
Any obsolute kernels that you installed with rpm you can remove with:
rpm -e package-name
You can do so even if you have already deleted the package's files in /boot and /lib/modules.
Of course, if you accidently delete a file that you need then you are screwed which is why you back everything up to tarballs on CD-RW before you start deleting files and also make sure that you have a working rescue CD.
Be prepared. Create a LifeBoat CD.