You can do that, but it probably will not get you a better image if it's already been sized down. In most kits, there will be a preview that's 600x600 pixels, 72dpi. That's the one you should use. Anything smaller is going to be insufficient for your folder preview. So just open that 600x600 preview in the "Preview" application, select all, copy, and then open the folder with "Get Info", click on the icon, and paste!
Originally Posted by agarzaldynrd