Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking dish.
Spread the blueberries evenly across the bottom of the dish.
In a bowl, mix the granulated sugar and blueberries gently.
Sprinkle the dry cake mix evenly over the blueberries.
Drizzle the melted butter over the cake mix.
Pour water and vanilla extract over the mixture.
Sprinkle cinnamon on top if desired.
Bake in the preheated oven for 45 minutes or until golden brown.
Let cool slightly before serving. Enjoy warm or at room temperature.