I am trying to change the color of my background which is a green screen to black. How can I change the color to black? I am using a Macbook air laptop.
You don't need to delete the background. A new adjustment layer will be automatically created above your original layer once you choose to add the adjustment layer.
You can choose green or cyan and use the eyedroppers. After using the eyedroppers the dialog box may change what it says, depending on which color it considers closest to what you've eyedroppered.
Is there a way I can make it darker without the creases showing?
The reason your background is not as dark as mine may be because the original photo is slightly different than the screen capture that you posted, or it could be that you didn't eyedropper as much of the green area as I did.
You could select the Hue/Saturation layer. choose green or cyan from the dropdown menu (or whichever color the Hue/Saturation dialog box used) and use the Eyedropper Plus+ to select more of the green area. Drag over the area you want, including some of the folds. That should take care of it.
But if it doesn't, you can duplicate the Hue/Saturation layer.
In the layers panel, click the Adjustment icon and choose Hue/Saturation.
Double-click the Hue/Saturation to open the dialog box and choose Green from the list.
Use the Eyedropper tool in the Hue/Saturation dialog box to click on the green area. Use the Eyedropper with a '+' to click and drag over more of the green area.
Then drag the Lightness slider all the way to the left.
The model has a slight green reflection in the hair, glasses, skin. You could go over those areas with the Sponge tool set to Desaturate.
The green reflection can pretty much be avoided in the first place by photographing the model further away from the background green screen.