uname -r 
> 4.4.0-139-generic

sudo dpkg --list 'linux-image*'|awk '{ if ($1=="ii") print $2}'|grep -v `uname -r`
> linux-image-4.4.0-134-generic
> linux-image-4.4.0-138-generic
> linux-image-4.4.0-141-generic
> linux-image-4.4.0-97-generic
> linux-image-extra-4.4.0-134-generic
> linux-image-extra-4.4.0-138-generic
> linux-image-extra-4.4.0-141-generic
> linux-image-generic

sudo rm -rf /boot/*-4.4.0-{97,134,138}-*
sudo apt-get -f install -y
sudo apt-get autoremove -y
sudo update-grub && sudo apt-get update

df -h
/dev/sda1               461M  227M  211M  52% /boot