Try factory reset using Volume UP+Power key. Power off your phone and press that keys. When BLU logo appears release the power button and keep pressing Volume UP key until Recovery mode shows to you. Then using the Volume UP and Volume DOWN key , choose factory reset/wipe data and press that with power key and then click YES. When that finish , press Reboot system. This could help
Maybe because he is full with cache, maybe too much applications and private things like photos,videos music. I recommend you to backup all data and factory reset him. This could help to improve your perfomance.