To delete one or a few contacts, click the checkbox next to their name from your Contact Management page and select More Actions and Delete.
To delete an entire list of contacts, click Email Lists from the left column and click the trash icon for the list you want to delete. You will be asked if you simply want to delete the list and keep the contacts or delete the list and associated contacts. To permanently delete the contact, click Delete the list and contacts.
To delete all contacts. click the checkbox at the very top of your list to select all, then select More Actions and Delete.