Per ora funge cosi perchè ho seguito questa guida
Using the Vol button, highlight WIPE DATA/FACTORY RESET.
Once done, highlight WIPE CACHE PARTITION.
Normally this is enough for a normal reflash but if your recovering from a problem or an issue and want a really really good clean up, perform these optional steps:
Select MOUNTS AND STORAGE
Using your vol and power button:
format /cache
format /data
format /system
Select +++++Go Back+++++
Select Advanced
Wipe Dalvik Cache
Reboot Recovery. This step is quite important and your phone will as it says reboot, so don't worry, just let it do its thing.
Wipe Data/Factory Reset once more.