Comment 199 for bug 798414

The solution is listed in ubuntu documentation.

first check space of /boot

>: df -h

>: sudo apt-get autoremove

this should freeup some space and 90% times this will resolve your issue.

if you have manually installed and still the old files are not purged follow the link below

https://help.ubuntu.com/community/RemoveOldKernels

this still works for ubunt 22.04 /boot folder issues resolution, cleaning /boot folder removing older files