PDF (adobe.com)

Rotate or flip an entire image

The Image Rotation commands let you rotate or flip an entire image. The commands do not work on individual layers or parts of layers, paths, or selection borders. If you want to rotate a selection or layer, use the Transform or Free Transform commands.

Rotating images

A.
Flip Horizontal

B.
Original image

C.
Flip Vertical

D.
Rotate 90° CCW

E.
Rotate 180°

F.
Rotate 90° CW

 Choose Image > Image Rotation, and choose one of the following commands from the submenu:
180°
Rotates the image by a half-turn.

90° CW
Rotates the image clockwise by a quarter-turn.

90° CCW
Rotates the image counterclockwise by a quarter-turn.

Arbitrary
Rotates the image by the angle you specify. If you choose this option, enter an angle between ‑359.99 and 359.99 in the angle text box. (In Photoshop, you can select °CW or °CCW to rotate clockwise or counterclockwise.) Then click OK.
Note: Image Rotation is destructive editing and actually modifies the file information. If you want to non-destructively rotate the image for viewing, use the Rotation tool.