Is your belt too long? Are you in-between sizes? Aaron Marino of alpha m. gives a step-by-step demonstration for how to customize your belt length.
The belt needs a metal end and a leather end. If you turn the belt over, observe the little screws. Once unscrewed, the leather comes out. Cut this end of the belt to the length necessary, reinsert, and screw to secure. You can use the screwdrivers that are used with glasses or use tweezers. Paperclips also work. Just because you find belts that are too long or you are in-between sizes, you can customize the belt and nail that center hole.