Download 3 (maybe 4) debs to a folder somewhere:
linux-headers-VERSION-NUMBER_all.deb
linux-headers-VERSION-NUMBER_amd64.deb
linux-image-VERSION-NUMBER_amd64.deb
linux-image-extra-VERSION-NUMBER_amd64.deb # if available
Install the debs with whatever package manager front-end you use (is gdebi still around?), or use these commands:
cd /path/to/folder/where/you/put/the/debs
sudo dpkg -i *.deb
sudo update-grub
sudo reboot now
Choose the deb files above depending on your i386 or amd64 bit OS version
References
http://askubuntu.com/questions/119080/how-to-update-kernel-to-the-latest-mainline-version-without-any-distro-upgrade
