To revert to the latest recommended kernel:
sudo apt-get install --install-recommends linux-generic-hwe-18.04
To maintain the kernel and cleanse the unused:
You should check partially removed kernels with
dpkg -l linux-image-\* | grep ^rc
and remove them with for example sudo apt-get purge linux-image-4.4.0-101-generic.
Purging will remove initramfs generation rules from /var/lib/initramfs-tools/.
If it does not help, you can remove them manually from initramfs list:
sudo rm /var/lib/initramfs-tools/3.13.0-39-generic
sudo rm /var/lib/initramfs-tools/4.4.0-101-generic
sudo rm /var/lib/initramfs-tools/4.4.0-103-generic
sudo rm /var/lib/initramfs-tools/4.4.0-38-generic
sudo rm /var/lib/initramfs-tools/4.4.0-45-generic
sudo rm /var/lib/initramfs-tools/4.4.0-59-generic
sudo rm /var/lib/initramfs-tools/4.4.0-77-generic
sudo rm /var/lib/initramfs-tools/4.4.0-78-generic
sudo rm /var/lib/initramfs-tools/4.4.0-81-generic
Usually I run purge-old-kernels followed by sudo apt-get autoremove to have only 2 recent kernels.
You can reinstall installed kernels with their initramfses:
sudo apt-get install --reinstall \
$(dpkg -l linux-image-\* | grep ^ii | awk '{print $2}')