Step 1 - Locate the file
Step 2 - Right Click the file and select 'Rename'
Step 3 - Amend '.zip' to the end of the file and hit enter or attempt to open with a compression software such as winzip, winrar, winace etc
Step 4 - Open zipped folder and view contents
Cannot see '.zip'??
Go to the Tools menu in Windows Explorer (in the directory where the file is go to the tools menu or hit Alt on your keyboard then Tools will appear. Then go to 'Folder options....." -> "View" -> untick "Hide extensions for known file types" -> Apply. Remember this location so you can tick this box again so you dont mistakenly rename another file and dont know the extension to change it back.