You cannot delete a Customer, however, you can make the Customer INACTIVE. This action will remove the customer record from the list view.
Go to the Customers module
Locate and open the Customer record
Inactivate the record
Save
If you would like to re-activate a customer record, remove the 'Active' filtering on your list view to reveal all inactive records, open the inactive customer name (all inactive records are strikethrough) by clicking on it, then check the 'Active' box and Save.