In the Layers window,
ensure the display button at the top is set to Paint.
Select the paint layer, then double-click
the layer’s Opacity value and enter a new
value or click the opacity slider and move it up or down keeping
in mind the following
Increase the Opacity setting to
a higher number to increase the opacity of the image on the selected layer.
Reduce the Opacity setting
to a lower number to reduce the opacity of the image on the selected layer.
NoteBy default the Opacity setting
has a range between 0 and 100; Positive or negative values outside
this range can be entered to further amplify or invert the paint
information stored on the layer.