There are two ways to delete Library tags.
From the Call Card
When you want to remove a tag from a curtain call all you have to do is click the "trash" icon next to the tag. If you do not have the "trash" icon, it means that you do not have the 'remove tag' permission for the library.
Delete Tag from a Library
To delete a tag from a library you'll need to go to the Library tab.
*if you have admin access to the Library you should see a 'manage' button
Scroll down to the bottom of the pop-up and you should see all of the tags associated with your Library. To delete, just click on the 'x' beside the tag.