Open the zip in something that will let you see what it contains (most archive applications will do that) and use that as a guide to deleting files.

Are you sure you have textures and props in the same place - there should be .png image files with many items, which are the tumbnails you see in the Content palette (items which don't have .pngs may have .rsr files instead, which do the same job but are a special, hard to edit, format).