And your layers palette should look like this. Lighter image on top, darker on on the bottom.
Next you're going to select the bottom (darker) layer and select the highlights (cmd-opt-~ on the Mac, ctl-opt-~ on the PC). This will select the highlights of the darker image, leaving a bunch of "crawling ants" to show you what you've selected.
After you've done that, click on the layer above, and click the add mask icon at the bottom of the window (the white circle in gray box). This will create a mask for that layer, but that mask will be the opposite of what you want, and you'll need to invert it (cmd-i on the Mac, ctl-i, PC). Now you should be seeing the highlights from the bottom layer showing through your uppermost layer.