If two plots are displayed, first set the plot you want to access the settings for as active by clicking in it. Then push the F5-key or click the button found to the right on the Plot Toolbar. The settings can also be accessed from the Plot->Plot Type Settings->Active Plot…. A dialog box will appear displaying the settings for the plot type. All settings (except layout settings) should be available from this dialog.
Note: the button displays the settings for all the frequency domain plot types. If a setting in this dialog box is changed, it will thus affect all the frequency domain plot types.