1. You can use "Shift+click and drag" to zoom into a specific window or location
  2. You can use the +/- keys on your keyboard to zoom in around the center of the range, both X and Y.
  3. You can place the cursor where you want to center the zoom window and roll the mouse wheel.
  4. You can right click outside of the X or Y axis line and find a new Zoom/Pan and Autoscale menu.
  5. You can right-click and select "Setup Options" and from the top "General Plot Options" section, check the box for "Autoscale across plots of same type" to make both plots scale together.
  6. You can right-click and select "Reset Scale" to return to the default scaling
  7. Somewhat of a "trick" answer, but you can "minimize" windows you do not want to see by clicking the carrot (^) in the upper right-hand corner of the plot. This will essentially enlarge the plots you do want to see. While not technically changing the scale, it can make it easier to view the data you are most interested in.