You can ban or delete any of your site users within 'Manage' and then 'Members'.
Select who you will want to ban/delete from the list of members and click their tick box. Click the 'Change Status' drop down and select a status for that user. Click the submit button to confirm the change.
The user will now be banned/deleted etc from accessing the site.
You can make banned or deleted users active again by selecting “Active” from the Change Status drop down menu.