That's not a Mac issue, but a router issue. The usual procedure:
1. Connect wired.
2. Go to your browser.
3. In the address bar type the IP-address of the router. That's in the user manual.
4. Then login with the right usernaam (that's in the user manual of the router) and the right password (that's in the user manual of the router, unless you did reset it, then it's in your notes or in your head).