You can change how much the image moves when you click the scroll arrows or press the Arrow keys.
To change the size of the scroll step:
1. Choose View ® Options.
2. Click Window.
3. In the Step Size text box under Scroll Bars, type by what percentage of the current view you want the image to move with each mouse click. Click OK (or Set All).
Each time you click the scroll arrows or use the Arrow keys, the image will move the defined amount.