Remove your Old Kernel On Ubuntu
When you’re running Ubuntu and updating your system frequently, there is a high chance that older kernels that are no longer needed are still installed on your system. Over time, if these older kernels are not removed, precious hard disk space may be wasted and your system’s performance may suffer.
Open terminal and check your current kernel:
root@penreturns:~$ uname -r
Next, type the command below to view / list all installed kernels on your system.
root@penreturns:~$ dpkg –list | grep linux-image
Find all the kernels that lower than your current kernel. When you know which kernel to remove, continue below to remove it. Run the commands below to remove the kernel you selected.
root@penreturns:~$ sudo apt-get purge linux-image-x.x.x.x-generic
root@penreturns:~$ sudo update-grub2
Reboot your system.