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

Hi,

For testing purposes I've created some demo questions and answers in my site, http://bit.ly/1RATZ6w, 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?

Thanks.