Do you know how to log onto your router? As already stated the default IP is probably in your manual. Open up your browser and type in
http://192.168.2.1 (or whatever your router's IP is). If you post the make and model of your router you may get some pointers on what to look for but some routers are fairly intuitive. If you don't have a manual then google the make/model.... there's bound to be info out there.