There are four files to download, go to https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.4.2/ download:
linux-headers-5.4.2-050402_5.4.2-050402.201912042231_all.deb
linux-headers-5.4.2-050402-generic_5.4.2-050402.201912042231_amd64.deb
linux-image-unsigned-5.4.2-050402-generic_5.4.2-050402.201912042231_amd64.deb
linux-modules-5.4.2-050402-generic_5.4.2-050402.201912042231_amd64.deb
These are the 5.4.2 upgrade to the file you want to download, and upgrade other versions to find the corresponding file.
Then execute
sudo dpkg -i *.deb
Then you can restart.
Download time to pay attention to look at your system is 64-bit or 32-bit, or processor is not the ARM. Do Wrong.