Second hand iPhone Troubles?

I bought a second hand iPhone from eBay, but it previously belonged to someone else. The phone is linked to the Apple ID of the old owner and I don't know it. Is there a way for me to still use the phone?

Iphone 5 Software Update Issue iOS 8.3?

I have an iphone 5. I'm having some trouble installing the iOS 8.3. I go to setting > General >Software update > Install now > Then agree > But nothing happens. It just takes me to the front page. I have checked my usage I have 4.6 GB left. I have pressed restart but I that changes nothing. Does anyone know how I can fix this issue?