Apple release first time iOS Beta for All users forever, recent iOS 8.3 Beta 4 version, users can install in device without developer account. Might be reason is that Apple watch supporting features also covered in recent Beta version on iOS 8.3, So why you missed the chance for upgrade from iOS 8.2 to iOS 8.3 on your iPhone 6 and iPhone 6 plus. Continuously WatchKit API improvement and Siri language features improvements made most of the folk’s expectation true. If you know that Apple watch will be release on 24th April by syncing your iPhone only through iOS 8.2 or later version and Compatible iPhone Model (iPhone 5S, iPhone 6 and iPhone 6 plus). You can get the whole story update on latest iOS 8.3 Beta 4 from developer. Here I covered thinks before upgrade with iOS 8.3 from older iOS 8.2, iOS 8.1.
Steps to Update or upgrade from iOS 8.2 to iOS 8.3 in iPhone
Step 1: Verify you have done Backup as you wise in correct way, Go to the iTunes and Launch it in your Mac/PC (Check latest version on iTunes).
Step 3: From the top side navigation choose Device you connected through USB lighting cable with your Mac/ PC.
Step 4: Now iTunes will verify your device have new iOS version or Not So Click on “Check for Update”.
Step 5: Further instruction come on screen if updates available. If yes then you will see the popup with option “Download and Update” by agree with terms and Condition/ Unlock Passcode on device (Message will appear on iTunes careen if applicable in device), you can start iOS update automatically.
Once Process on update iOS done, for upgrade from iOS 8.2 to iOS 8.3 beta 4 (Recently might be rename with new bug fixed and more). if you can’t comfort and facing error on use then you can downgrade back in to older iOS version (iOS 8.2 not beta).