When you select 'Semantic differential' as the Question type, you will get an empty table with two label columns at either end, and a five-item scale in the middle:
Very much |
Somewhat |
Neither |
Somewhat |
Very much |
To change these column headers, just click somewhere in the column, and then on the button. You can also double-click on the column header. This will make a text field appear, where you can modify the name of this class (column).
If you want to add a class (column), click in the column to the right of where you want to insert it. Then press the button in the toolbar.
If you want to remove a class (column), click in the column itself and then on the button.