From an address book, select the contact to be removed, and click 
on the toolbar.
Drag the contact name to the Trash folder.
Right-click on the contact and select Delete.
Contacts can be deleted in one of three ways:
From an address book, select the contact to be removed, and click on the toolbar.
Drag the contact name to the Trash folder.
Right-click on the contact and select Delete.
Note: If you delete a contact that was automatically added to your address book, the contact is moved to the Trash folder. You cannot add the name back to your address books until you delete the contact from the Trash folder.
Any contact lists you create can be deleted.
Right-click on the contact list you created and select Delete.
When contact names are deleted, they no longer appear in your address book and information is not available from the name tool tips for the address auto-completion or from the address search dialog in the mail compose window.
Note: If you delete a contact, you can immediately undo this action by clicking the Undo link that appears at the top of the page. The contact is moved back to its original location.