moved your topic here :), not an update problem
so your mirror list is on /etc/pacman.d. this is a sequential list, so the first address is the first used by pacman. you can comment line which doesn't work.
Anyway, you can install and use reflector to update the list
$ sudo pacman -Sy reflector
$ sudo reflector -l 20 --sort rate --save /etc/pacman.d/mirrorlist
see reflector man pages to know how to use it