To find out the current version of Linux kernel running on your system, use the following command.

<code>$ uname -sr

Linux 4.12.0-041200-generic
</code>

To list all installed kernels on your system, issue this command.

<code>$ dpkg -l | grep linux-image | awk '{print$2}'

linux-image-4.12.0-041200-generic
linux-image-4.8.0-22-generic
linux-image-extra-4.8.0-22-generic
linux-image-generic
</code>


Run the commands below to remove a particular linux-image along with its configuration files, then update grub2 configuration, and lastly reboot the system.

<code>$ sudo apt remove --purge linux-image-4.4.0-21-generic
$ sudo update-grub2
$ sudo reboot</code>

And that's it.