Deleting a Textbox in PowerPoint

If you want to remove a textbox from a slide:

Click on the outer frame off the textbox, so the handles (small white circles) appear as figure 1-1
Press the Delete key on your keyboard

Fig 1-1: Textbox clicked to show the handles

Figure 1-1

If you find that you are deleting text within the textbox, rather than the textbox itself, you have clicked inside the textbox, rather than its frame, if this is the case as figure 1-2

Fig 1-2: Text box showing cursor in text instead of frame

Figure 1-2

Click outside the textbox, to deselect it and click back on its frame so the handles appear
Make sure that the cursor is not flashing in the text of the textbox, or you will have the same problem again (note the difference between figure 1-2, which has the cursor at the end of the text and 1-1, which does not.)
Press the Delete key on your keyboard

You will find the textbox disappears from the slide. If it does not, re-examine the previous points.