Removing a user from "Users with Highest Reputation Points" widget


For testing purposes I've created some demo questions and answers in my site,, I've also voted some of those answers.
My problem is after deleting those demo questions and answers the "Users with Highest Reputation Points" sidebar widget still shows a one demo user with reputation points.

How can I remove this user from the sidebar? Do I need to change his reputation in the database? If so can you tell me how to reset the database step by step?