Since we already have a selection we're going to get rid of a certain part of the selection and keep the part that we want to keep. 

Choose Subtract from Selection from the options bar.

Now go ahead and create a lasso selection all the way around the area that you want to get rid of from the overall selection. It doesn't even have to be pretty AT ALL, as long as you keep the marching ants inside the area.

Just work your way all the way around the area you want to deselect. With the polygonal it will draw straight lines and you click to add a point to move it in another direction. What's weird and cool is that you can click ‘outside of' the actual document with the polygonal lasso to help work your way around to the start point to close it off. Try this out for yourself.

Now that you have ‘subtracted' or ‘deselected' that area...

...find any other areas that you want deselected, go over there and use the same method to enclose off that area to deselect it from the overall selection.    

In this case I am getting rid of the dead palm tree leaves and wanting to retain just the main subject herself.  It's important to understand these concepts of knowing how to modify a selection.

Now with the moVe tool, remember that you can move the selection from within the selected area. In this case we already have a duplicate layer on top so we're just moving that selected version of her over.

Here you can see in the layers palette I've turned off the layer and you can see the selection that we've made.

Go back in History to move her back. You can also use Edit: Undo Move.

Now let's do something else. Once you have a selection you can save it a few ways. One of the ways is by right clicking (when on the appropriate tool such as lasso) and choosing Make Work Path...

This will convert the selection you have into a ‘Path'. Under the Paths palette you can see the work path that you've now created.

A path is one way of ‘storing' your selection (in this case) and takes up a nanobit of space in the total file size because it is basically a mathematical equation. It saves much more space than duplicating and retaining a copy of the layer (fyi).

You can see the hard edged line of the 'Path' around your subject when you have 'Work Path' highlighted in the Paths palette.

Aren't you glad you don't have to learn all this stuff the hard way? Don't be stubborn like I did. Just keep on learning everything you can with tools like the Basic Photoshop DVD training of mine. It's loaded with tons of Photoshop training for your educational needs.

Once you have work path you can make it back into a selection by highlighting it and then right clicking and choosing Make Selection...

Press enter again if you don't want to feather (add a light fuzzy blur around the edges) and get your exact selection back (recommended for now).  You can edit it as a selection or with the path editing tools.

In the Paths palette you can click off of the path and onto the empty space as shown to de-select the work path and click on it to re-select or show the work path.

Paths are also covered in depth in my full video training. You'll also want to understand them b/c you can make your own work paths (ending up in a selection or a custom shape) from scratch and they are used all the time in vector shapes and design.