There may be some setting named WAN configuration, you can edit the internet entry and change dns there. Post screenshots of that page (blur any id info).
What is WAN configuration and where will I find it? Will it be at the back side of the router?
My Netlink Router is this
When I tried to access router default login, it asked for admin username & password and when I gave admin as both usr & pw it did not login. Should I login the routers default login page and take a screenshot? Please reply.