Oh, well. The more I read about ubuntuhandbook.org here from users, the more I wish it would die instantly, because such low quality copypasta without explanation harms users.
See the section on Launchpad PPAs below for more details. (The package that the guide tells you to download is from Kernel Team PPA.)
Automatic kernel updates
You don't need to install additional kernel packages or external sources in Ubuntu. Everything is done for you automatically through the Software Updater. To be more specific, there exists a meta package that always points to the latest kernel that is available in this Ubuntu release.
Running saucy this is the current state:
$ aptitude show linux-image
Package: linux-image
State: not installed
Version: 3.11.0.12.13
Priority: optional
Section: kernel
Maintainer: Ubuntu Kernel Team <kernel-team@lists.ubuntu.com>
Architecture: amd64
Uncompressed Size: 33,8 k
Depends: linux-image-generic
Conflicts: linux-image
Provided by: linux-image-3.11.0-11-lowlatency, linux-image-3.11.0-12-generic, linux-image-3.11.0-8-generic
Description: Generic Linux kernel image.
This package will always depend on the latest generic Linux kernel image and headers.
If you run another Ubuntu release, that is not End of Life (EOL), don't fear, you are still covered and receive security patches and bugfixes for your kernel automatically.
Other kernels