Whenever you update your system, new available kernels get installed and the preexisting ones do not automatically give way to the new ones. This eats up a lot of memory. Here's how to remove them.
In terminal(Main Menu > System Tools > Terminal) enter the following command to get the full release version of the kernel.
# rpm -q kernel
to remove a version enter:
# rpm -e kernel-version
using the rpm command will also clean up your grub.conf.
CAUTION: Keeping the old kernel is for backup if something goes wrong. So, be careful.
