You do not need to download ANY third party software or even connect your phone to computer to remove any screen lock on your phone.
You will lose all data on the phone following the steps below:
You simply turn off the phone (If you are having difficulties just hold power + volume down + home to force shut down phone). Hold volume up + power button and home button. Stop holding the power button + home button + volume up button when the Samsung logo appears and/or a blue text at the top left of the screen says booting to recovery.
Once it has booted to the Android recovery use the volume up and down keys to select / highlight a option.
Select the wipe data / factory reset option and use the power button to select this option.
Edit: If it asks for a Google and or Samsung account and password, it means the device has FRP (Factory Reset Protection) lock enabled which you can bypass using the method provided here:
You can additionally downgrade from Android 7.0/7.1.2 Nougat back to Marshmallow 6.0.1 (IIRC maybe also 6.0).
If the method linked does not work there are plenty other methods which you will need to look around for.