Your router's settings are accessed via your web browser.
With your router connected via an ethernet cable (that's the bright yellow or orange one which should have come with the router) open your web browser (Internet Explorer, Firefox, Chrome, etc), type the relevant 'dotted quad' (like the numbers suggested by Rojash) into the browser's address bar and click 'Go'.
We can't tell you what the required 'dotted quad' is without knowing the make of your browser. (When you do manage to get into the settings you'll encounter a password field. If you've never set a password on your router you can usually just leave it blank).
Chris