Refer to the following article re: instructions on how to mark a machine for removal: http://copiun.helpserve.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=7
For security reasons, Copiun administrative GUI doesn't permit immediate deletion of machine data. If you'd like to delete data for some machines immediately, please contact Copiun Support via support@copiun.com.