If you are having trouble removing items from your library please check to see if the item is currently being using in a message.
Follow the steps below to completely remove the items.
Click the check box next to the items or multiple items you want to delete.
Press trashcan/delete icon.
You may receive this message.
Navigate to your Messages tab on the left menu.
Check the Sent, Drafts, Archive and Trash tabs for the message that contains the item you want to delete.
Any items deleted are moved to the Trash tab.
Make sure to empty the Trash as well.
After completely removing the message you can return to the Library and delete the item.