Open the report in design view. Locate the Line, double click(left) to bring up the properties view. Click on any of the properties and make changes as you usually would, looking into any dropdown menus and selecting the setting you want or by entering a value. To delete the line just hit the delete key or backspace key while the line is highlighted.
You can make any changes and experiment then close without saving if you're not sure OR close and save if you are sure that that those are the changes you want.
Goh