For teachers, zooming should be done using your browser. My favoured method is holding down <ctrl> and then pressing + - and 0. Alternatives include holding <ctrl> whilst using the mouse wheel or pinching with two fingers. Some methods may be browser dependent. Failing that, if you go to your browser settings or browser view menu there is usually a 'zoom' option.
Also note that by sorting the vMini WhiteBoards appropriately, you should not need to see that many screens at once. Periodically pressing the 'i' key will perform an intelligent sort to bring the boards most needing your attention to the top. See the 'help' link just above your teacher mini WhiteBoard for details of various sorting options (there are several).
For the student display, it is recommend to use browser zooming as the primary method, but for devices where this is not possible or doesn't give the best results, (+),(-) zoom functions are provided.