Freeing up GBPVRUiElement's

[InVermont]

This is the gist of what I am trying

//class member vars
private Bitmap screenBitmap;
private GBPVRUiElement screenBitmapElement;

//in Activate, first run through
screenBitmap = new Bitmap(bWidth, bheight);
//draw on bitmap, add text, whatever
screenBitmapElement = new GBPVRUiElement("screenBitmap", startingLocationRect, screenBitmap );

//in GetRenderList()
renderList.Add(screenBitmapElement)

This all works like expected, displaying the bitmap. However, when I go to change the bitmap

private void changeBitmap()
{
using (Graphics g = Graphics.FromImage(screenBitmap)) {
//draw on it, add text, decide to move it around, whatever

}
screenBitmapElement = new GBPVRUiElement("screenBitmap", NewRect,
screenBitmap );
}

I think this bleeds memory, as I am not cleaning up the original screenBitmapElement, just pointing it to a new one.
I have tried variations along the lines of

using (Graphics g = ...

ArrayList disposeList = new ArrayList()
disposeList.Add( screenBitmapElement );
PluginHelper.DisposeResources(disposeList);

screenBitmapElement = new GBPVRUiElement("screenBitmap", NewLocationRect,
screenBitmap );

and it explodes.
How do I clean up the original
screenBitmapElement ? Do I need to?

Is there a better way of doing it?

thanks