1) Navigate into ..Steamsteamappscommondeus ex - human revolution (finding these folders depend on where you have Steam installed) and make a backup of patch2.000 though you can have Steam redownload it by doing verify integrity if you want the original file back.<br />

2) Unpack the download into the same folder, so you'll have a "new", modded patch2.000 file. If you don't need a backup, over-write the existing file.<br />

3) Play!