Sony Xperia Z3. What to do after major upgrade?

Wiping the Phone's Cache Partition:

NOTE: Assuming that your smartphone is not working as intended and you're thinking about master resetting it, then you might want to try and wipe the phone's cache partition first. Wiping the phone's cache can solve numerous issues without having to factory reset and lose all your personal data. To wipe the cache partition:

1. With the smartphone turned ON, press and hold the "Power" and "Volume Up" buttons
2. Wait for the display to turn off and for the smartphone to vibrate three times
3. When the smartphone's screen shuts off, release all the buttons
4. The cache partition should now be wiped. Press the "Power" button to reboot your Xperia Z3 as you normally would

NOTE: If wiping the cache partition hasn't solved your issues then you might want to consider factory resetting it.