Two techniques to try!
Fill up two Ziploc bags with water, and seal them tightly. Place the bags inside tight shoes, and let them sit overnight in the freezer, or until the water in the bags freezes. As the water freezes, it will slowly expand the bag to gently stretch the walls of your shoes.
Or stretch a pair of shoes by wearing thick damp socks and blow drying the tight areas.
Do It And How 