go to User -> Users. In the search text box enter any keywords such as user first name, last name, email, address etc. You could use Date Range to fine tune the results. Click "Go" button and you will be given a list of users matching the search criterias. Clicking the "Delete" button on the row of the customer that you wish to delete will delete the customer and all the orders that belongs to the customer. We don't commend to delete customer because your statistics could be inaccurate when the orders are deleted along with the customer.