Cleaning up old Ubuntu kernels from /boot

Get your kernel version

$ uname -a

List the kernel into /boot:

$ sudo dpkg -l linux-image-\* | grep ^ii

Uninstall the old kernel:

$ sudo apt-get purge linux-image-3.0.0-16-generic

WARNING: Don't remove the current kernel version!!

source: http://blog.niftysnippets.org/2012/06/cleaning-up-old-ubuntu-kernels-from.html?m=1