Adobe Photoshop - Images

[Zen C]

Hi,

I have a question on Photoshop. I am trying to highlight a change in a
screen (yup this is related with the release notes) and want to outline it
with a circle (outline a changed field with a circle). How would I do that
in Photoshop?

I used the shape tool buttons and could not get rid of the fill color and
then tried switching to Image Ready and sending to back as the help file
explains, but doesn't work for me.

I also tried clicking Edit>Stroke, cos I read it somewhere online, but it is
grayed out.

Help please.

Zen