The second part is useful and should stop the update from installing or prompting to install.Go to Settings -> iTunes & App Stores -> uncheck Updates.
Go to Settings -> General -> Storage & iCloud Usage -> Manage Storage -> tap and delete the iOS update file.
Delete the update from your storage as was suggested in an earlier post and that should prevent it from installing.my phone just popped up will update between 3-5am I don't want it to update. As I want to stay on my 10.3.1 for future jailbreak. How do I make it not update?