1) To select an image ( that contains a graph ) you can double-click on the right side close to of its field.
Once it is selected, the rectangular field appears lightly in grey.
Then you can copy it ( cmd c ) or cut it (cmd x ).
2) To change the color of the curve, or its line-style, or its color filling, its opacity … use the command Set Properties from the menu ( first pict ) and then select the curve and the surface you want to modify.
For the change from fig.1 to fig.2 I colored and white ( with opacity 100% ) the surface under the horizontal. Then change whatever you want (second pict )
For the change from fig.2 to fig.3 I changed the unit ( something like 1.5cm in place of 1cm ) and I introduced a cartesian grid.