boot - How to replace or remove kernel with signed kernels

Whenever I am updating ubuntu getting following error message. The message is asking me to remove or replace the current kernel version with the signed version.

How to do this?

Below is the message I am getting:

Your system has UEFI Secure Boot enabled in firmware, and the
following kernels present on your system are unsigned:

4.19.6

These kernels cannot be verified under Secure Boot. To ensure your
system remains bootable, GRUB will not be upgraded on your disk until
these kernels are removed or replaced with signed kernels.

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Following kernels are right now installed in my machine, which is listed by running command: dpkg --list | grep linux-image

1. ic linux-image-4.15.0-29-generic 4.15.0-29.31 amd64 Signed kernel image generic


2. rc linux-image-4.15.0-39-generic 4.15.0-39.42 amd64 Signed kernel image generic


3. ii linux-image-4.15.0-42-generic 4.15.0-42.45 amd64 Signed kernel image generic


4. ii linux-image-4.15.0-43-generic 4.15.0-43.46 amd64 Signed kernel image generic


5. ii linux-image-4.15.0-45-generic 4.15.0-45.48 amd64 Signed kernel image generic


6. ii linux-image-generic 4.15.0.45.47 amd64 Generic Linux kernel image


7. ii linux-image-unsigned-4.19.5-041905-generic 4.19.5-041905.201812031110 amd64 Linux kernel image for version 4.19.5 on 64 bit x86 SMP

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kernel version I am running, retrieved by running command uname -a:

Linux dipak 4.19.6 #1 SMP Tue Dec 18 10:30:34 IST 2018 x86_64 x86_64 x86_64 GNU/Linux

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Ubuntu distrubution version (lsb_release -a):

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.2 LTS
Release: 18.04
Codename: bionic