I accidentally selected to update my operating system to ios 7 , i stopped it halfway by disabling wifi but how to stop it completely??? iPhone 4, iOS 6.1.3

Yeah, this happened to me too. From my research, I found a sort of solution. You have to keep Wi-Fi disabled and connect your iPhone to your computer with iTunes. Restore your phone with your back-up. When you can access your phone's settings, turn off Wi-Fi since it will be enabled with the restore. As long as it is not charging, you should be able to continue using Wi-Fi and not be downloading the update. When you need to charge, make sure you disable Wi-Fi first.