Try hard resetting your router, by holding the reset button on your router for about 5 seconds. If you have the instructions for the router, you should be able to find the IP address and change the password using that.
On your pc go into start menu, run, then type in cmd and press enter.
This should bring up a command box. Then type in ipconfig and press enter.
This should bring up a set of numbers. Write down the default gateway number and type it into the internet where you would write a web address and you should be able access your router settings and change your password. When going into this it may prompt you for your login details and normally root for username nothing for password should work fine if nothing was changed.
Hope this helps.