Question [Q] Changing default alarm ringtone


I'm on Archidroid 1.7.15 which is, for me, the best rom until (hopefully) the port of Kitkat from the n7100 to our i9300.

My question is not crucial : i've looked for changing the default ringtone for the alarm but i haven't found the way to do that yet.
Is anybody know if it's possible and if yes, how to do that ?