Drag the middle mouse button to rotate the view about the center.
Choose View tab→Orient group→Rotate 
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A rotate tool appears at the center of the view.
Click an axis of the rotate tool, part edge, or endpoint on the model to define the focus of rotation. Click the origin of the rotate tool if you want to rotate freely about the center of the view.
Drag to rotate the view.
Tip:
When you are rotating the view about an axis, part edge, or endpoint on the model, you can type an angle value in the command bar box to specify a precise rotation distance. A negative value changes the direction of rotation.
You can use the arrow keys on the keyboard outside of the Rotate command, to rotate the view incrementally.
Press the Home key to return the view to an isometric orientation.
When you select an endpoint on the model, it becomes the origin around which the view rotates.