The equals sign means is equal to. It is telling us that one thing equates to another; that they are the same.
The iPhone 4 is the most recent iPhone to be discontinued from the iOS Update cycle. It did not receive the iOS 8 update, so it's final software version is iOS 7.1.2. You can update to this version through iTunes, or download it from an IPSW repository like this website: https://ipsw.me/.
We don't expect to see the iPhone 7 until the fall of 2016, so it's quite a ways off. Apple just released their 2015 models, the iPhone 6s and the iPhone 6s Plus.