A neighbours friend turned up today and he called me over. His friend has a Halfords Carrera E Bike. He had a puncture and needed an inner tube etc, so I helped. He asked me if I knew anything about E bikes, I said 'no'. He wants to change the bike from a 300 watt to a 500 watt. I understand that this would entail changing the back wheel and possibly the battery. What do I need to know to be able to do this for him? I don't mind doing it as it's a bit of a project and I enjoy bike maintenance, but if I will be way out of my depth, I'll pass.