There's a long explanation behind your first question. Ask the exchange to give you a new line from the ONU.
You can change your DNS for every device connected to the router or for your PC only. Typing it out will take forever so you can Google it, a very easy process.
But if you want the entire router to use a different DNS, typing that out will take even longer. So, you can download TeamViewer, let me take over remotely and set it up for you. It'll take a total of about 5 minutes.
Sent from my SM-N910F