A cowboy hat can come in a variety of materials. Leather is a very popular option but it is susceptible to wear and tear, so you must take proper care of your hat to make it to last. If you properly shape and size your leather cowboy hat, you can maintain the cowboy look without endangering the hat.
Buy a hat form or wig stand in the correct size for your head. You will find these tools at hat and leather specialty shops; consult with an expert at the store if you are unsure about your hat size.
Lightly dampen the head band of the hat (or the area that needs to be shaped) in warm water or hat-shaping spray. Do not thoroughly wet the hat, as water will stain or damage leather. If you are unsure about using water, try using a small amount of rubbing alcohol; this will dissolve faster, but will also leave your hat smelling for a few days.
Set the dampened hat on your stand so that it conforms to the appropriate size. If you are shaping the hat as well as resizing, be sure to adjust it to the shape you want while it is still damp. Allow the hat to dry completely in a cool, shady area, out of direct sunlight and away from heat sources. Sunlight and heat can warp or stain the leather.
Try on the hat to see if it has conformed to the correct fit. Repeat the dampening and stretching as needed until the hat fits. Do not try to rush this project, as the leather can be easily damaged by mistreatment.