My Samsung Galaxy A3 keeps rebooting

[AC Question]

I just got my new Samsung Galaxy A3 today and i updated the android to lollipop and whilst its trying to optimise 192 apps half way through it reboots all the time, not allowing the apps to be optimised. Please help. Its going midnight in my country and the phone keeps making the boot up sound. If nobody can help with this problem can you please tell me how to turn it off whilst in an endless reboot because the Samsung Galaxy A3 doesn't have a user removable battery. Thank You.