Here is a quick set of commands to clean up the /boot partition on an Ubuntu linux system.
First check what your kernel version is so you won’t delete the running kernel image:
uname -r
Now run this for a list of installed kernels:
dpkg --list 'linux-image*' | grep ^ii
delete the kernels you don’t want/need anymore by running this:
sudo apt-get remove linux-image-Ver
Replace the “Ver” with the version(s) of the kernel(s) you want to remove.
Finally, run this to update the grub kernel list:
sudo update-grub