Hello and welcome to the iMore forums, simply go into (Assuming you are using a Mac) iTunes and Option click restore iPhone (while your device is connected) ... Select the ipsw file and it will update. Please note that if this is the 7.1 beta you will need to have your UDID registered in the Developer Portal. However you should be able to install iOS by simply utilizing the software update feature on your 4s .. This will download the current non-beta version to your device directly.
If your phone is currently working their area lots of UDID apps in the App Store that will email your UDID to you. To me that's a very simple solution. You could also attach the iPhone to your Mac and look in the system profiler which will show the iPhones serial number which is the same.