Update Jailbroken Iphone
With any Jailbroken device, any update of any kind will break the Jailbreak. OTA updates (update from device in settings app) will kill your phone and force a restore. Updating through iTunes will revert the Jailbreak but leave the rest of your data untouched. I recommend updating to 8.4 and jailbreaking again with the new TAiG jailbreak tool (plus it gives you some laughs during the process because the translation is so horrible)!

Hope this helped, Nick