Double-click on the layer name Background, and click OK.
Under the Select menu, choose the Color Range… command.
Using the Eyedropper tool that appears, hold the SHIFT key while clicking
and dragging around all the green area you want to remove. Click OK when finished.
The ALT key de-selects, if needed.
Under the Select menu, choose Inverse
Under the Select menu, choose Select and Mask while holding
the Shift key. You can use the various sliders to adjust the
smoothness of the edge of your cutout. Click OK when finished.