You
can modify saved selections by replacing, adding to, or subtracting
from them.
Make a selection in your photo.
Choose Select > Save Selection.
In the Save Selection dialog box, choose the selection
you want to modify from the Selection menu.
Select one of the following and click OK:
Replace Selection
Replaces the saved selection with the current selection.
Add To Selection
Adds the current selection to the saved selection.
Subtract From Selection
Subtracts the current selection from the saved selection.
Intersect With Selection
Replaces the saved selection with the intersection between
the current selection and the saved selection.
You
can also modify a saved selection by loading it and using selection
tools to add to it (Shift-drag) or subtract from it (Option-drag).
(See Add to or subtract from a selection.)