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First, run the following command to remove outdated linux headers: 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

Kept back packages