Ubuntu : How to Remove Old Kernels From Ubuntu

Solutions:

1. Check current running kernel version. #uname -r
2. Check list of installed Kernels on your system. #dpkg --list | grep linux-image
3. Find out the kernels you want to remove. #sudo apt-get purge linux-image-x.x.x.x-generic

Source :

http://ubuntuhandbook.org/index.php/2013/08/remove-old-kernels-from-ubuntu-13-04-13-10/