if you cannot login to the router page using the default login password to the router console page that means someone has changed the initial login setup.
In this case you can only get the router reset to factory default then you can login and make changes in ssid and password
after reset router will have no security password you can set it up anytime you want.
Implication of reset:
If you reset you router you will loose all the connections to the devices which has wifi, however after the reset the router should boot up fine and there will be no security to the router i mean it will connect without prompting for a connection password. you need to get the router secured using wep or wpa. I will give you steps to secure it.
Reset the router to factory defaults.
Reset the router to factory defaults and once connected wifi we can get the router security setup.
use a paper clip, look at the back of the router you will see a tiny reset button,
Push and hold down the button for 10 seconds while the power is on using the paper clip.
release the button and wait for 2 to 3 mins for the router to boot up
Now connect to the internet and try scanning for available wireless network as you see the router name and try to connect. It will not have any security password to connect.