You can rotate an image and all its contents by 90 or 180 degrees, or freely. You can also flip images vertically and horizontally.
Note: These options rotate and flip the entire image. To rotate or flip individual layers, see Resize, rotate, and flip layers.
To rotate the image together with the image canvas:
To rotate the image independently from the image canvas:
You can also click Rotate in the Tool Options pane to rotate the image by 180º, or 90° to the left or right.
Also, with the Crop tool selected, you can click Flip Horizontally to flip the image horizontally or Flip Vertically to flip it vertically.