Don't feel too upset when you get the post-upgrade iOS blues, there's a few things you can do

    You are not a victim, so if you woke up with the iPhone blues this morning try these simple solutions to see if they help.

    Slow iPhone?

   Sometimes subsequent to installing an important upgrade you may find your iOS device runs slower than it did before the upgrade was installed. Sometimes this is only temporary as the device indexes its contents and builds up a fresh version of its Spotlight search files – you also see this this behavior in OS X subsequent to some, but not all, upgrades. (Apple could make this more predictable by letting users know if an upgrade is likely to trigger such behavior).
     Patience
   In most cases it makes sense to sit back and let the process complete, it usually takes a few hours which is why it makes sense to upgrade your device last thing at night, rather than first thing in the morning when you’ve got an essential conference call scheduled. (You may also see battery life temporarily impacted while this process takes place.If time and patience don’t seem to do the trick, then please remain calm and try the following steps.
     Force Restart
   Always try this step if apps become unstable or the device otherwise becomes less reliable than usual: Hold down the sleep/wake and Home buttons both at once for at least 10-seconds until the Apple logo appears on a black screen.
   Reset
   Open Settings>General, select 'Reset' and then choose 'Reset All Settings'. This won't delete anything (bar your WiFi password) but might help mitigate performance problems.
    Still got problems?
   Restore: The most time-consuming patch and you must have a recent backup before you begin. Connect your device to iTunes and choose the Restore option in the top pane within Summary view. The device will be returned to factory condition. Restore is often the most effective troubleshooting step, but you will need to reintroduce all your apps, log into all your services and reapply passwords and any customized device settings you may use. 
   Make it new
If the problem continues then try a full restore once again, only this time do not restore from backup.
   Recovery mode
 You can put your iOS device into recovery mode, then restore it:

With iTunes

• Turn your device off and plug your cable into your computer, but not your device.
• Hold down the Home button on your device as you connect the cable. Keep holding the button until the Connect to iTunes screen appears, release the Home button.
• iTunes will launch and say it has detected a device in recovery mode.
• Now use iTunes to Restore your device, doing so in recovery mode will erase your device. 
• In the Summary panel choose Restore iPhone, then choose Restore in the following dialog box. Your device will restart once the operation is complete, and you’ll get to set it up as new. Alternatively, if you have a back up here is how to restore from your backup.

Without iTunes

To reset iPhone without iTunes Tap Settings>General>Reset>Erase all Contentand Settings, and provide the passcode if needed. You may need to turn offFind my iPhone if this is enabled.

I hope these few suggestions help you get through your experience of the slow iPhone blues – in most cases such problems are temporary.