When you need to delete a bunch of layers, it's overly tedious to have to delete them one a time. Here's a way to delete all those unwanted layers at once:
First make all the layers you don't want visible and make all the layers you do want invisible. Next select one of the visible layers and use the Merge visible option (access it from the pop menu that comes up when you press on the little right-pointing triangle at the top right of the Layers palette). Then delete the resulting layer and make the layer or layers that you want to keep visible again.
