Updating Kernel is Simpler than you think
First of all you need to go to the site where you can download the kernel file of Linux

Index of /~kernel-ppa/mainline

What you can see is the list of available Linux Kernel Version
what you need to do is pick the kernel that you want to use (for me I used v5.12-rc6)

You can opt between low-latency and generic files.
If you want the low-latency kernel than download that, instead go only for generic files such as :

  • linux-headers-x.x.x * low-latency
  • linux-headers-x.x.x *_x.x.x_all.deb
  • linux-image-unsigned-x.x.x * low-latency
  • llinux-modules-x.x.x * low-latency

For generic download the generic Debian packages for the kernel.

  • linux-headers-x.x.x * generic
  • linux-headers-x.x.x *_x.x.x_all.deb
  • linux-image-unsigned-x.x.x * generic
  • llinux-modules-x.x.x * generic

However, one will be common in both generic and low-latency is the Linux-headers-x.x.x*_all.deb
The x.x.x in this case will be 5.12.0

Because we have downloaded from the browser

$ cd Downloads

and while avoiding to install the deb files by one by one we will use the command

$ sudo dpkg -i *.deb

after this done and your system rebooted

$ uname -sr

you will be able to see the updated kernel version