In your grub configuration file, remove the entry for the kernel you want to remove, save the changes and reboot. Be very sure that your new kernel works (I usually give about a months practice before removing a working kernel from my machine). Then in /boot remove the kernel that you removed the entry for, and if you really want to get sick with it remove the entry for that kernel's modules in /lib/modules/kernel-version where kernel-version is the kernel that you removed. You can also safely remove the old kernel's sources if you had/have them in /usr/src/kernel-version and be sure that you have properly setup the new symlink to the new kernel sources:
ln -sf /usr/src/kernel-version /usr/src/linux (rememer this is the NEW kernel)
To make sure everything checks out before actually "deleting" or rm'ing everything, I usually make a directory in /tmp called kernel:
mkdir /tmp/kernel
And move everything there. Then, if upon reboot everything is working, I'll go ahead and delete the directory (hopefully you don't have /tmp autocleaned upon reboot, if you do, use another directory for the temp backup
).
Cool
