How do i find out a user's password?

hi.
so, a while back, i started playing this online fps. and i have two computers. so u can see the advantage.
on the other computer (not this one) the internet only works for one user. and i have to find out what the password is.
is there a way for me to do that?
i heard that cmd is really good for that kind of thing.
btw, i am not looking to change the password at all. i just need to find out the password.
preferably, i would not like to download anything.

ps. the other computer has two accounts. mine(which doesnt have internet) and the other one (which has internet)
mine has full administrative powers. so yeah.

Step by step instructions are always useful.
Thank you

 

You don't.

Passwords are there to keep people who don't know them out of something.