How do I change my iPad Pro screen from landscape to portrait

From the Apple User Guide: http://help.apple.com/ipad/11/#/iPad997da805

Change the screen orientation

Many apps give you a different view when you rotate iPad.

Lock the screen orientation. Open Control Center, then tap [Lock Icon with an Circle around it].

When the screen orientation is locked, [Lock Icon with an Circle around it] appears in the status bar.

On iPad models with a side switch, you can also set the side switch to lock the screen orientation instead of silencing sound effects and notifications. Go to Settings > General. Below “Use Side Switch to,” tap Lock Rotation.