How to Remove All Unused Linux Kernel Headers, Images and Modules

Use the following command to remove

dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs sudo apt-get -y purge

#Then regenerate grub menu,
sudo update-grub to regenerate grub list

Credit goes to original source