Rotate your selection using the rotation handle located on the right hand side of the shape. Click and hold down the left mouse button on the rotation handle and drag the selection to a desired position.
A selection’s rotation handle
You can also rotate a selection using the Rotate command in the Image menu or by using the rotation wheel in the Tool Settings Panel.
Rotation dialog
Rotate a selection using the Tool Settings Panel
To use the rotation wheel grab the knob and, without letting go of the left mouse button, rotate it to any degree. You can also rotate the image by clicking on one of the preset arrow buttons or typing in a degree yourself and hitting enter.