[otrs] How do I remove Customer Users ?

Hi, I am running OTRS for the first time and would like to know how to delete Customer Users. I am logged in as the Admin user and have entered the Customer area. I can search on users with "*", select the users in question and change their "Valid" status to "invalid". I can not however find how to remove them. OTRS 2.02-01 MySQL 4.0.18-log Apache 2.0.49 RedHat Linux 9 (Shrike) Any advice is appreciated. John.