Adjust the Graph Actual Size/Scaling Button

Click the button to display the Document Size and Scaling dialog

and change the current graphs aspect ratio (i.e., the ratio of its vertical to horizontal dimensions). Note that the global default graph aspect ratio can be modified on the Graphs tab of the Options dialog (accessible via the Tools menu).

The modified proportions of the graph will also be reflected in the printout (as can be examined using the Print Preview facility, use the Print Preview   toolbar button or select Print Preview from the File menu).