Well, you have to extract your wad first. Click at the yellow symbol behind the line of "Select one of the GP4's wad to patch or the wad to extract" (this yellow symbol might be concealed, just make the window fullscreen and it appears). Then a window which asks for a wad-file appears, just search and select the wad you want to extract. Then click "Extract wad", then another window appears and asks for a folder were the extracted wad will be located. Just use the same folder as where the cars.wad is in, just copy the cars.wad of GP4 in an own folder before extracting. Now click save and WadUpdater will extract the wad. Then you go into the folder where the cars.wad was extracted and you click at "cars", then there are "cars", "fonts" and "maps" and you click at "cars" again, then you see a list of many files. You have to rename the downloaded helmet textures with "driver_xy_1/2.tex" and replace the other files (maybe make a backup of the original files!). Then you go out of the folders and back to WadUpdater, click at "Select a folder" and choose the folder with the cars.wad, then click at "cars" (don't go deeper than one time cars, because you need all three folders (cars, fonts and maps) inside the new cars.wad as well, so don't choose the second cars as well!). Then click "Create wad" and another window appears asking you where the file will be saved. When choosing the same folder than the old cars.wad will be overwritten by the new one. WadUpdater will display when the wad is ready for use and how long it took the program to create it, usually this are only 5 to 10 seconds. Then don't forget to put the new cars.wad in the GP4 directory. And then you should hopefully have the new helmets in the game.