Edit > Application Preferences > Edit > Rotate

• Angle step
  The rotation angle.
• Shift multiplier
  Factor that is applied to the angle when the Shift key is pressed while rotating.
• Alt multiplier
  Factor that is applied to the angle when the Alt key is pressed while rotating.
• Center of Rotation
  This preference only has an effect when rotating a selection.
  • Centroid of convex bounding polygon (default):
    The center of rotation is always in the same location at about the center of a selection. With this preference, rotations are reversible. This means that a selection that is rotated clockwise and then rotated back counter-clockwise is back at the same position again.
  • Relative zero point:
    Rotate around the current location of the relative zero point.
  • Center of bounding box:
    Rotate around the center of the bounding box of the current selection. This type of rotation is not generally reversible.