Two options. On your PC do a right mouse click and click properties. On your phone, if you have a file manager (Astro, Root Explorer) tap and look at the extension
gunny, in windows explorer when you are looking at the file does it look like this: ChevyNo1-1.1Ghz-lowV-7slot-update.zip or like ChevyNo1-1.1Ghz-lowV-7slot-update without looking at the properties just a straight open windows explorer and navigate to the directory where you saved the file. Just trying to help.