Which password do you need to change? The password to enter the routers settings or the password for the wireless network ?

To change the password for the router you need to know the current password so you can go into the router and change the password.
If you don't know the routers current password then you have the push the reset button on the back of the router and reset it to factory spec's. Then you can use the default user name and passwword to enter the routers internal settings.

If your wanting to change the wireless password then you have to go into the routers internal settings and go to the wireless section and the wireless security sub-menu and there you will find the password that you used for the wireless network.