Do you mean the router's login password or the encryption password?
To reset the Linksys back to the default settings - Press and hold the pinhole RESET button at the back of the router with the power ON for 20 secs. then release the RESET button.
To connect to your wireless router, the router's wireless settings needs to be configured with the SSID, encryption etc. and also the wireless cards in all the laptops/computers needs to be configured with these router's wireless settings. Then the laptops/desktop computers can communicate with your wireless router.
Connect a LAN cable from the Linksys to the LAN port on your computer.
Open a browser and enter the Linksys configuration URL
The default login = admin
The default PW = admin
You can protect your router by changing the default admin PW (write it down and put it in a safe place)
Go to the wireless configuration and set up the SSID and WPA or WPA2 encryption.
Now apply these settings to the wireless card in your laptop/computer.
To secure your wireless network from unauthorized access, please click on this link and follow my instructions :- http://www.fixya.com/support/r3559128-wireless_router_security