Deleting programs from Mediabox is quite straight forward but is done in two steps to avoid any current and published content from accidentally being permanently removed.

Content can only be deleted from the 'Archived programs' section so to delete programs, you first have to archive them. See How do I archive programs? for information on how to archive.

Once archived, programs will appear in 'Archived programs'. This is where you delete a program or its contents.

Delete a program
Go do 'Archived programs' and find the program you want to delete. Click the settings icon next to the program title, season or episode (depending on what part/s you want to delete).

Choose 'Delete' in the drop down menu. A modal will appear asking you to confirm that you want to delete the item. Click 'Delete'. 

Once deleted, the content can not be retrieved.