You can both navigate and zoom image using one of the options.

Navigation/Zoom toolbar icons

Arm (A) and Zoom tool (Z) is located on the Toolbar right above Pen tools.

Zoom Shortcuts

To Zoom In hover the pointer over the image in Editor or Result and move to the left holding the mouse button down or press (CTRL++/Command++)

To zoom out press the mouse-button and move the pointer to the right or press (CTRL+-/Command+-)

Navigator dialog

Navigator enables you to (a) zoom, (b) navigate the image, (c) switch between  Editor and Result, (d) enable/disable Scale Synchronization between views.