You are able to delete contacts from your subscribers, one-at-a-time or in bulk, whenever you wish. However, you must be very careful when deleting contacts -- it is a completely permanent action, and cannot be undone, in any way.
When deleting from your subscribers, we recommend that you always export the list or contacts that you will delete, even if you are 100% sure that you want to delete them. It's always better to have a back-up that you don't use, than to need a back-up that you don't have.
Always check twice, before deleting contacts from your subscribers. Once you've clicked that trashcan button, there's no going back.