Zoom:

Menu + Mouse: Using the menu commands (View > ZPR > ZPR or View > ZPR > Zoom), keep the left mouse button pressed, move the cursor up to zoom in (increase the size) and down to zoom out (decrease the size).

Ctrl + Mouse: Zoom by pressing the Ctrl + Right Mouse button. Zoom as above; move the cursor up to zoom in and down to zoom out.

Mouse Only: This "ZPR Mode" can be automatically invoked by pressing the left mouse button for a predefined duration (this functionality is defined in the Preferences). When the ZPR Mode cursor is displayed, zoom as above; move the cursor up to zoom in and down to zoom out. Exit the ZPR Mode by pressing the Esc key or the middle mouse button.