Sticky notes can be deleted using the Comments catalogue which will also remove them from the document.

Alternatively:

  1. Select the Hand tool  on the Edit toolbar
    or the Sticky Note icon  on the Commenting toolbar (View > Toolbars > Commenting).
  2. Click on the sticky note icon to select it.
  3. Press Backspace or Delete on the keyboard. Alternatively, right-click on the sticky note icon and choose Delete.