For some reason,
sudo apt-get autoremove often does not remove a lot of the old kernels. One will need to manually remove them if you are running out of space on your
sudo apt-get purge linux-image-x.x.x.x-generic
x.x.x.x with something like
3.13.0-63 when you see
initrd.img-3.13.0-62-generic listed in /boot.
When you are finished removing kernels, be sure to update your grub boot loader.