edit pacman.conf with nano in a terminal
sudo nano /etc/pacman.conf
add the repo of your choice to the end of the file. Each of the 3 repos has a kernel you can install. Most people use liquorix for gaming and linux libre to avoid drm stuff like to play netflix videos.
[herecura]
# packages built against stable
Server = https://repo.herecura.be/herecura/x86_64
[liquorix]
Server = https://liquorix.net/archlinux/$repo/$arch
#[libre]
#Server = https://repo.parabola.nu/libre/os/x86_64
After you install do:
sudo pacman -Syu {your kernel and} {headers}
you will get an error asking if you want to import the keys. STOP and do nothing in that window for a moment.
OPEN a new terminal and run
sudo pacman-key --recv-keys {the key from the other window}
sudo pacman-key --lsign {the key from the other window}
after they both finish close that terminal and go back to the other terminal
it's still asking if you wish to import the key. Respond 'Y'
after your kernel is finished installing run
sudo update-grub
when that finishes run
sudo reboot
choose advanced options from the grub menu to choose the kernel you wish to boot
easy, peasy, mac and cheesy
if you install linux-libre from the repo as above rather than build it from source from the aur say, then it will replace your default linux kernel, headers, and firmware.