How do I delete content from my nookColor?

In general you don't want to delete material you want to archive it. View the item details and select "Archive".

You can't delete the content B&N puts on the nookColor (Guide, etc) for some reason. 

If you want to really remove the item (book sample, free book you hated, etc) checkout the user guide or follow these steps:

The item should now be gone.