How can I delete a text box in a Pages document?

The depends if it is a text box that you inserted, or a locked x text box in a template. In the first instanced, you click outside of the text box to ensure it is deselected, then click once on it and press the delete key. In the latter case, you click once on the locked text box to select it and then on the Arrange panel, click UnLock, then press the delete key.