iPhone 5c issues with backup and update

i have tried to back up my iPhone 5c and it says error cannot back up or it will say backup error incomplete or something like that. I've tried everything from going on iTunes on the computer and trying to update my phone and back up my phone that way but it says the same thing. I've deleted half of my stuff to update my phone and back it up but it still says error. I don't know what to do I've tried everything from resetting and have done sign out of iCloud it still doesn't work. All I'm trying to do is back up my phone and save everything in the iCloud on the computer so I can get a new phone. My phone is also a iOS 8.4.1. But I've just given up and can't find a fix to it so I would like to know how I could fix this problem? So I can get a new phone.