Lollipop Upgrade Error

Hi Friends,
My friend upgraded his A5 to Lollipop 5.0.2..the software download was successful.. when he installed it, it reached 100% but said an error occurred.and that the phone needs to be restarted. He didn’t do anything yet because immediately the android avatar appeared with the words “Downloading. Do not Turn off target”…he decided to reboot it and followed the instructions online. But the only choices were to continue downloading the custom OS or cancel and restart phone…but either way still the same thing appeared..he cant do anything..how does he reboot/reformat it?…or how does he resolve this without rebooting? Thanks in advance.