The rotate layer can rotate the image and all preceding layers by any amount. Add a Rotate layer by clicking the Rotate icon on the Edit tab of the toolbar.
You can rotate the image by clicking and dragging on the image or by setting the rotation in the properties panel.
Click the left button to rotate the image 90 degrees counter-clockwise.
Click the center button to rotate the image 180 degrees.
Click the right button to rotate the image 90 degrees clockwise.
The Rotation (degrees) number field can be used to rotate the image by any arbitrary angle.
Check the Crop corners checkbox to remove excess blank space.