ok locate your layers menu window... default is in the bottom right of the screen.
select the layer caled background. most likely it will be locked. to edit it do the following.
right lick on hat layer and got to duplicate layer. hit ok on the pop up window
now select the background layer again.
now right click and select delete layer... this will eliminate the orgional backround lar allowing you to edit the new layer.
now with the back ground copy layer selected go to the top of this mini window and go to opacity and change this to 0% givin u a transparent background.