Check the existing kernel of your Ubuntu Linux:
Ubuntu maintains a website for all the versions of kernel that have been released. At the time of this writing, the latest stable release of Ubuntu kernel is 4.15. If you go to this link: http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15/, you will see several links for download.
Download the appropriate files based on the type of OS you have. For 64 bit, I would download the following deb files:
Install all the downloaded deb files:
sudo dpkg -i *.deb
Reboot your machine and check if the kernel has been updated by: