"The volume "boot" has only 0 bytes disk space remaining" error

Very simple

sudo apt-get autoremove

This will delete those unuseful kernels in /boot.

ref:
https://ubuntuforums.org/showthread.php?t=2239126
https://askubuntu.com/questions/345588/what-is-the-safest-way-to-clean-up-boot-partition