To quickly and easily delete multiple contacts, you can import them as a Delete List. Go To Contacts > Import Contacts > Delete Contacts:
You will need to create a .CSV file for these contacts in order to import as a Delete List. This will mark any contact on the list as deleted and they will show a status of Unsubscribed. If you ever re-import these contacts as a regular list, they will become active again as long as they have not unsubscribed themselves from your newsletter.
You can also manually select contacts in any list and delete them: