Step 1 - Check if your style has an adjustable sweatband. The cotton strap in your sweatband can adjust the size up or down. Learn how it works Adjustable Strap Video
Step 2 - If you don't have an adjustable sweatband, you can try out Hat Fillers for the perfect fit. Perfect if your hat is slightly too big.
Step 3 - If your hat feels too big for either of these options, you can return it for a different size. You can find all the info you'll need on returns at https://willandbear.com/a/returns