Summarize this article:

Stretch your shoes overnight by filling them with water, then freezing them. The easiest way to do that is to place a resealable plastic bag that’s about halfway full of water into the shoe. Make sure the bag is sealed tightly so you don’t spill any water in the inside of the shoe, as this could damage the insole.  If you're concerned the bag might break, use 2 bags instead, placing one inside the other.  You can try this with any type of shoe, but it might work better for open-toe, peep-toe, or athletic styles. If the toe box on your shoes is very narrow, it might be hard to arrange the bag so it reaches all the way down into the shoe, and it might not stretch evenly. Leave the shoes in the freezer for several hours or overnight. Give the shoes enough time to make sure the water is frozen completely solid. Putting your shoes on a tray or a baking sheet will keep the bottom of your shoes from touching a surface your food might come in contact with. You can also place them into a large bag or on a sheet or parchment paper. However, you can just put them directly into the freezer, if you want. Once the ice is completely frozen, take the shoes out of the freezer. Leave them in a warm, dry place for about 15-30 minutes, or until the ice starts to melt. Then, wiggle the bag back and forth until you can remove it from the shoe. It’s better not to let the ice thaw out all the way. If there are any holes in the bag, the water could leak into the shoe and damage it.

Summary:
Fill a resealable bag halfway with water and place it in the shoe. Place the shoes onto a tray and place the tray in the freezer. Leave the shoes at room temperature for 15-30 minutes, then remove the bag.