You can delete content items from your Authory account anytime. Here is how:
Go to the respective content item's detail view
Click on the "Settings" option in the top bar menu
Select "Delete" from the dropdown
You can also bulk delete multiple content items at once: Go to your Content section, select the items you want to delete, then click delete in the blue action bar.
Another option to bulk delete is to delete the entire source in your Source settings. Deleting a source will delete all content items that have been added to this source, so please be careful when deleting a source.