Summarize this article in one sentence.
If you want the new belt hole to be as tidy and discreet as possible, a leather hole punch is by far the best tool. These typically cost less than $10 US at a craft or hobby store. Bring along your belt when shopping, to compare the size of the punch with the size of the existing holes. The punching tool tip should fit tightly through the existing holes. If you have many belts to adjust, look for a rotary model with a wheel of attachments in different sizes.

Summary:
Purchase a leather hole punch.