In order to Unsubscribe or Subscribe a contact, navigate to the Contacts Tab -> All Contacts Tab -> Click On The Specific Contact you are trying to Unsubscribe or Subscribe:
Once you are inside the Contact's Profile, click on the More button under the Contact's Details.
This will open a small menu where you can see a button to Unsubscribe a contact:
You can also subscribe users in bulk from the Contacts tab by filtering, then selecting all the contacts you want to Subscribe or Unsubscribe them and clicking on More.
Then you can select whether you want to Add Contacts To List or Remove Contacts From A List.
This will either subscribe/remove contacts from the list you are attempting to modify:
