Graphs can be closed singly or all graphs that are currently displayed can be cleared from the workspace.
To close a single graph
Click the Clear button 
on the graph window or select Close <Ctrl+F4> from the System menu.
To close all graphs
Select the Close All option from the Graphs menu. All the currently displayed graphs are closed. (If the Close Prompt option is selected on the Options menu, you will be asked to confirm this command before the graphs are closed.)