At the same time, old kernel remains in the system. It means that after some time of using Ubuntu, you may have a number of old kernels. They take your disk space and also may clutter the GRUB menu, although the latter issue is resolved in newer versions of Ubuntu.
This video shows you the way to remove old obsolete kernels from your Ubuntu installation.
The same approach is valid for whole Ubuntu family and derivatives: Xubuntu, Edubuntu, Kubuntu, Zorin OS, Linux Mint and so on.
Please remember that the "best practice" is to keep at least two kernels in the system: the current and the previous one. This is to ensure the fallback solution if current kernel fails for whatever reason.
How many old kernels do you have in your system? How often do you remove the obsolete kernels?