It's easy. Simply guess the correct password. Failing that, contact the person who originally applied the password. If you're looking for a super password that will supercede anything the original programmer put in place, you're out of luck.
While I personally don't use passwords, I respect the right of others to use them. Consequently, when they are applied, I don't condone attempts to bypass them. As I see it, there are two reasons why you don't know the password. Either the original programmer didn't want you to have it or you failed to make acceptance of the system contingent upon delivery of the password to you. By "you", I mean your company, not necessarily you personally.