If you are a hub admin you can delete the posts or replies from any other members. Deleting posts is not available on mobile devices. There is a small icon to the lower right of all posts, click it to see a menu where you can delete or edit any post. If you are not the hub admin you can only delete your own comments. 

After another user replies to your comment you will no longer be able to delete it since it would also remove their comment.

One of the benefits of Spokt is that after a while you have a rich history of conversations with your group. It really is great to go back and re-read past conversations.