All transformations are performed around a fixed point called the reference point. By default, this point is at the center of the item you are transforming. However, you can change the reference point or move the center point to a different location using the reference point locator in the options bar.
In the options bar, click a square on the
reference point locator . Each square
represents a point on the bounding box. For example, to move the reference
point to the upper left corner of the bounding box, click the top
left square on the reference point locator.
In the transform bounding box that appears in the
image, drag the reference point . The
reference point can be outside the item you want to transform.