When you installed your router it should have come with a manual. It might be on paper but it's more likely to be in a PDF (or HTML) file on your PC. The instructions for accessing your router settings should be in there.
My router settings are accessed via a local web page. I enter 192.168.2.1 into the address bar of my browser, and then click 'Go'. (That takes me to a login page). My router is from Belkin. If you've got the same make, the same URL should work. However different makes of router require a different address to be entered into the browser. If you can't find the manual (which should tell you how to access the settings), try googling the name of your router, together with 'settings'. Alternatively, post again and I'll see if I can find the relevant information.
Chris