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

uname -sr

Linux 4.19.0-8-amd64

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

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

linux-image-4.19.0-6-amd64
linux-image-4.19.0-8-amd64
linux-image-amd64

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

sudo apt remove --purge linux-image-4.19.0-6-amd64
sudo update-grub2
sudo reboot