find a store near you. bring in your old and/or current pair. be prepared to get on a treadmill to be filmed for a gait analysis if they offer it, and i hope they do. they will then fit you to the proper class of running shoe.
FYI - do not(!) go by brand. do not take what someone else uses, unless they also require the same class of shoe and train for the same distance, have the same shaped foot, same gait, same leg lengths. the wrong class of shoe can actually cause more aches and pains and not relieve any.