If you have picked
linux-lts during install, then you are having BOTH kernels and you should see them before booting so you can pick the one you d like to boot with. In this case, default is the vurrent kernel and the lts is in the “advanced options”.
If you have not, then, you can install it now. Fire up a terminal and
sudo pacman -S linux-lts, or just look for the same package in pamac gui software manager. In this case, the lts kernel will be your default kernel and the current one will be in the “advanced options”.
It might be a good idea to install
linux-lts-headers , as well.
Using the lts kernel does NOT mean downgrading kernel. It is a more stable kernel because it s conservative and more suitable to older harware. Curent kernel, on the other hand, is more suitable mainly if you are on the latestr hardware .