If you need to reconfigure or reset your router, there are a couple ways of doing it.
First, if you don't care what's on the router, or if you can afford to screw it up before you make it better, then just reset it. Performing what's called a hard reset on any router will restore it to default settings. This will mean you will have to know how your router connects to the internet cause you'll have to change the settings yourself to make it connect to the internet again. It will also be reset to its default name and password etc.
It's very simple and easy to do. Basically you want to find a little button at the back of your router. This is the reset button. Find a paperclip or pin or something equally small, and push it into the small button. Hold it for about 30 secs. You should probably have a computer or iPod or some wireless interfacing device handy so you can check. A laptop would work best. Once you've pressed down the button, unplug the router and wait another 30 secs and plug it back in. Now look on your wireless device (ill assume you're using a laptop), at the wireless networks. What was previously yours will be labeled as its default name. If it's a Linksys router, it'll be called "Linksys" etc.
Now to reconfigure it, you'll need to connect to the network. Once you're connected, go to a web browser (my personal preference is Firefox). Type 192.168.1.1 into the address bar. 192.168.1.1 is the usual IP for your router. If it's not, then look at the properties of the network your connected to. You can usually find it. Once you connect to the router, it's probably going to ask for a username and password. Try the combinations of admin, admin, admin blank, root, etc. You can very easily find default passwords on the internet. Now you'll be at the router configuration and you'll have to reconfigure your router. You should call your ISP and find out what the network is (PPoE or otherwise) and how to connect. Your ISP should be able to direct you through the process.
If you can't afford to mess up the configuration on the
router, or if there are restrictions on the router you want to anonymously
change, then read the article: http://www.infobarrel.com/How_to_Recover_a_Router_Password