A magnification slider control is in the tool bar at the bottom of the microscopic image. The last button on the right toggles to full-screen.

To change the field of view, hold down the left mouse button and drag the image.

NOTE: The *overall* apparent magnification of a virtual slide is equal to the slide's "objective magnification" (either 20x or 40x, depending on the slide) multiplied by 10. The additional 10x magnification is equivalent to the 10x "eyepiece magnification" of a conventional microscope.