Most routers have some type of combination of hitting a recessed reset button while turning it on to reset the router back to default, check your manual, if you don't have it check the company's website for a copy of the manual.
For my SBC DSL modem/router, I actually had to call SBC to get it reset. I was kind of surprised since most routers will let you reset by hand, as DarienA said. If you have a company-issued combo router/modem, you might actually have to call 'em up.
It's a D-Link. DarienA anwsered my question for me. My Dad is claiming that the wireless network I setup in the house isn't working anymore and the I put a password on the router (I know I didn't) since I'm not there to configure the router I just figured that he can start from scratch and then re-do it.