Explains itself. Drag things [by "things" I mean the Acsessories and Faces]. towards the squishy. The Green-Screen doesn't just start green for show, it's so you can edit like a video or picture and make the Green-Screen what ever you want it to be. [Orrr, you could do it the easy way and add in your own Backdrop and change the maximum on the Green-Screen Slider].
Credit to: Squishies!!