as arch linux is a rolling release distro you will always have access to the mainline latest things directly from the official repo
else kernel as it get patch and need manual intervertion.
you can directly get latest from official arch linux repo or compile it yourself like from the thread (starting at git step) or just using aur (arch user repository) by using pikaur -S retroarch-git
retroarch present in image must be from official repo
meaning do a normal system upgrade will update it as well
so only one command by ssh :
sudo pacman -Syu
edit > sure as it’s a rolling release it may need time to time revert things or wait update 
but yet still suported and fresh after some years