Straighten
Have you ever squeezed off a quick shot only to discover that the horizon or another major element wasn't horizontal? Using the Straighten tool, you can easily correct this occasional problem.
Open a picture for editing, click the Basic Fixes tab, and click the Straighten button. A grid is superimposed over the picture, and controls appear at the bottom.
Drag the slider at the bottom of the picture to rotate the image. You can use the grid lines to help you horizontally align on any component. When you're satisfied, click Apply.
Note:
Straightening a picture crops it at the same time. If key elements are at the edges of the crooked photo, you may lose them.