1. Right click on the field that is duplicating and select Format Field.
2. Select the Common tab.
3. Select the "Suppress if Duplicated" option.
 

OR

1. In left most column of duplicating section, Right click and select "Format Section".
2. Select the Common tab.
3. Select the "X+2" button next to the "Suppress (No Drill-Down)" option and enter the appropriate formula to eliminate duplication.