After any update with your iOS devices you will receive number of common errors , when you update latest version iOS for your idevices, are you face with following issues and you can get instruction how fix this issues.
Common issues and how to fix it
1 battery life
2 related tThese issues more often than not vanish once the product settles down inside of a couple of days of the upgradeo the power consumption.
If you faced some struck when installing iOS 8 version you can fix this issue with few step
First restart your device and reboot , after you will can complete the installation of new iOS 8.4
If you have some problems with Wi-Fi and you ave to fix this issue and do this step
Resetting you’re your network settings Go to Setting -> General -> Reset Network Settings.
Navigate to setting -> Wi-Fi -> select your conection and check it is working.
If is it not working yet try with do this rebooting your router and modem -> Unplug and plug them back and after recheck.
This also Wi-Fi issues this or resetting Go to Settings -> General -> Reset -> reset all seting
First you try with restart devices and try toggling cellular data off and on again like this Go to cellular -> Cellular data -> Toggle off.
Other solution of Go to Settings -> Cellular -> Enable LTE -> Off wait few time when turn it back again and check.
Foe this issues Go to Settings -> General ->Reset -> Erase all settings and content.
you can do this not work it properly Go to Settings -> Messages -> toggle iMessage off.
If you need you can use other fix reboot off the network settings Settings -> General -> Reset -> Reset Network Settings