Choose Tools > Zoom (from the Tools menu at the top of your screen).
Press Z on your keyboard.
Do any of the following:
In the Tool Options pane, drag the Zoom slider to zoom in or out of the image. You can also use the Navigator box to change the area of an image on which you’re zoomed in.
Click the disclosure triangle next to the current zoom to choose a default zoom percentage, or type in a custom zoom percentage into the percentage field.
Under Mode, select Zoom In or Zoom Out and click the area of an image that you’d like to zoom in or zoom out.
Zoom using the scrubby zoom
In the Zoom tool options, you can use scrubby zoom to zoom an image by clicking and dragging over it.
To turn on scrubby zoom do one of the following:
In the Zoom tool options select Scrubby Zoom.
When a different tool is selected, press and hold Space + Option ⌥ on your keyboard.
Drag left or right on the canvas to zoom in and out of an image.
Tip: If you'd like to zoom by dragging your pointer on a vertical axis instead, you can use the Terminal app on your Mac to change the default behavior. You can enter the following Terminal flag or learn more about using Terminal on a Mac: