The image that you will work on in this tutorial is an image of the leaning tower of Pisa that I sourced from Wikipedia.
Select the crop tool in the tool panel.
Adjust the cropping shield
When the mouse button is released, the crop shield covers the area outside the crop selection.
Adjust crop marquee
In the image window, move the pointer outside the crop marquee so that it appears as a curved double arrow. Drag (rotate) clockwise until the tower is at the angle that you require it.
You may just want to watch the video I created.
This tutorial is less than one minute.