AirMore is the best file managing and transferring app I've ever used. It is 100% free, and I've been using it for over two years. It is an app that allows to transfer music, videos, photos, and other files from PC to iPhone or Android and vice versa. Everything can be done in seconds. How helpfule it is!
Also, on the "More" tab on phone, you are allowed to transfer files from phone to phone. (Also a little bit hard to find this feature, it is useful.)