What can I do if my leather boots are too big?

You can try shrinking them so they'll fit your feet better. Fill up a spray bottle with hot water and spray the outside of your leather boots. Make sure they get nice and saturated with the water. Then, take a hairdryer and set it on low speed. Hold the dryer about 6 inches (15 cm) from the boots and move it back and forth to blast the hot air over the surface. As the boots dry, the leather will shrink and the boots will get smaller. Be careful not to hold the heat of the hairdryer over 1 spot for too long or you can ruin the leather. Once they're fully dry, rub some leather conditioner into them so they won't crack or peel.