Whether you upgrade your i Phone 4 to i OS 7 is up to you, of course, but I'd be cautious.
If you upgrade, you'll be putting the latest OS, which requires a lot of processing horsepower and memory, onto a device that's approaching the end of its usable life.
Released on 8th June, 2015, i OS 9 comes up with subtle design changes, improved functionality, refined features and performance enhancements.
It also includes a Wallet app with store, an updated Notes app, a new News app, transit directions in Maps and loyalty cards, and an optimized battery backup.
The latest i OS available for the i Phone 4 is i OS 7.1.2 Have a look at: Maximum Supported i OS Version The direct download links for the full releases are: i Phone 4 (GSM Rev A) i Phone 4 (GSM) i Phone 4 (CDMA) Download the appropriate file for your device and then in i Tunes select the device and option-click the Check for Update button and select the downloaded file.
Also, if you Google "how to install ios from file using itunes" (without quotes) you'll find additional information. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
So you now have the latest firmware and be able to use an unlock solution such as Ultrasn0w or Gevey SIM.
You can also upgrade it for i Pad Air 2 and i Pad mini 2 and 3 efficiently.
Would you like to answer one of these unanswered questions instead?
While updating to the latest i OS firmware does have quite a number of advantages, not everyone is willing to take the plunge as there are bound to be negative consequences.
This is especially true when it comes to jailbreak users and to i Phone owners who are relying in an unlock solution.
The latter is especially affected because a firmware update will update their baseband thus rendering their device unusable in terms of phone functions.
In this tutorial we will teach you How to Update i Phone 4/3GS To i OS 6 While Preserving Baseband Using Redsn0w, which should definitely come in handy for unlockers.