====== Remove old kernels ======

==== Kernel headers ====

First, run the following command to remove outdated linux headers:
  # apt-get autoremove

==== Kernel images ====

Do not remove the current kernel, which you identify with:
  $ uname -r 

List all installed kernels on your system:
  # dpkg --list | grep linux-image 

Remove selected kernels:
  # apt-get purge linux-image-2.6.xx-xx-server

After removing a kernel, update-grub is called automatically. Do call in again manually:
  # update-grub2 

Reboot your system.

==== Check whether all kernels have been completely removed ====

Check the following directories:
  /usr/src
  /lib/firmware/2.6.xx-xx-server
  /lib/modules/2.6.xx-xx-server
  /var/lib/initramfs-tools/2.6.xx-xx-server
  /boot

[[http://askubuntu.com/questions/601/the-following-packages-have-been-kept-back-why-and-how-do-i-solve-it|Kept back packages]]