You are going to have to remove the Factory Reset Protection that is built into Samsung phones. To do this you will need to install and start sidesync on your PC (http://www.samsung.com/us/sidesync/), then begin the activation process on the phone by connecting the phone to WiFi. Once you get to the point where Google asks you to verify your information, use a USB cable to connect your PC and Android phone.
From that point, you basically have to unplug the device then sideload an application with updated Samsung apps using your browser from https://goo.gl/93nCX5. You will also need to 1.) install a file explorer app, and 2.) create a Samsung account or sign into your existing account. You can install ES File Explorer using your Samsung account once you have created it.
1. Open ES File Explorer.
2. Go to downloads and open the app that you just downloaded. (You will have to allow "unsafe" installations in your settings).
3. Go to your file explorer and enter "google account manager."
4. In list of folders, click on "google account manager - type email and password."
5. Click on "try" then click on the menu dropdown in the top right and click on "browser sign in."
6. Enter your Google account info.
7. Restart phone.
8. After it restarts click "next" until you get to a screen with "agree" then click that.
9. You will see that an account has been added. Click on "next, " then click on "restore from backup."
10. Click on "setup a new device" then hit "next" and "skip" until you get to "backup and sync," then click "later."
11. Click later to avoid fingerprint setup.
12. Click on finish.
13. You should now be able to go into your settings under "backup and reset" and perform a factory data reset.