well.. in your layer pallete it should be a button who says Normal.. There you can Find overlay and Softlight
At the right you got your layers pallte, there you will see ''NORMAL'' click on that thingie and you will see overlay
Go to layer, followed by blending options and you find overlay in there along with the other blend styles.
Yeah, just right click the layer. Choose blending options. Then a window pops up. There will be a bar that says normal..press that and change it to Overlay