Do you mean suppress them in the report? That will happen automatically when there's null data.
Or do you mean suppress the "label" or "column header"? In that case, right-click on the text object and select "Format Text". On the Common tab, there's a "Suppress" checkbox - leave the checkbox unchecked, go to the right of the screen and click on the formula button. In the formula put something like:
using the field whose data the label describes.