i have iphone 5c (gsm) model running 7.1.2, but I want to upgrade to 8.4. after much google searching, I find that I can do this supposedly by downloading the ipsw firmware for 8.4 and using itunes to restore it. however, because Apple only signs latest version (9.2.x), the 8.4 ipsw is not signed and therefore not able to upgrade it. I get an error from itunes saying that the device is not eligible for restore.
Is there an alternative method to force my iphone to 8.4 from 7.1.2?
my phone is not jailbroken yet, so wondering if maybe i need to jb first, then upgrade to 8.4
any help/comments is greatly appreciated.
thanks in advance!