Delete old unused linux kernel, images and headers.
echo $(dpkg --list | grep linux-image | awk '{ print $2 }' | sort -V |\ sed -n '/'`uname -r`'/q;p') $(dpkg --list | grep linux-headers |\ awk '{ print $2 }' | sort -V | sed -n '/'"$(uname -r |\ sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p') | xargs sudo apt-get -y purge