To Zoom the structure model in a View,
Click in the View to make it active, and spin the mouse wheel
To Pan the structure model in a View,
Hold down the Shift key, and click & drag the mouse in the View
To Re-center the structure model in a View,
Click in the View to make it active, and execute Display | mooZ
The Display | View Control command can also be used to Zoom & Pan the active View.