In Windows OS:
To zoom in: Hold down Crtl and then press +. Tap + until you are as zoomed in as you like.
To zoom out: Hold down Crtl and then press -. Tap - until you are as zoomed out as you like.
In Mac OS:
To zoom in, Hold control and scroll forward on the mouse wheel. To zoom out, hold control and scroll back on the mouse wheel. Note that sometime dust will creep into the mouse wheel and it won't function. To get around this you can utilize the keyboard command. To zoom in Hold Command Option and then hit Plus. To zoom out hold Command, Option and press Minus