Remove Old linux Kernels

 
Find out which version of the kernel that you are running:
uname -r

sudo apt-get remove linux-image-4.4.0-72-generic
sudo apt-get remove linux-headers-4.4.0-72-generic

Of course replace 4.4.0-72-generic with your kernel version number.

cd /var/lib/initramfs-tools

Remote old kernel file from this folder
then run the following:

/usr/sbin/update-initramfs -u -k all