In your version, if you press Ctrl+i then click anywhere on the graph you will be in the zoomed in view where you can use the scroll bars to pan around the graph. The mouse scroll wheel assists with vertical panning.
In 8.6 you can do much better since the A key now turns the mouse into a zoom/pan tool which works with the mouse by click and drag or the mouse wheel (or +/- keys) to zoom in and out or the arrow keys for directional panning.