The BEFW11S4 is ANCIENT HISTORY. It does not, as far as I know, support WPA, it hasn't had a firmware update in over a year, and it's pretty yucky to boot.
If you don't remember the password, then you can reset it to factory defaults (which include NO wireless password) by holding the reset button for 30 seconds
while you turn it on.
And go to
Linksys' page for the product to find the manual so you can read up on it. It's an easy thing to manage, but really you should spend the $50-70 to buy something from (literally) this century.