How to change the default passphrase?

how do i change the default passphrase ?, i used this command from terminal as the guide tells me:

Change the passphrase for the hard disk encryption by running “sudo cryptsetup luksChangeKey / dev / sda2” in a terminal. This passphrase is different from your user acount’s passphrase.

but it doesn’t make me change

What is the error message or the genreal output of the command?

thanks anyway, I solved;)
oh one new problem, i can’t connect wifi, … maybe it depends on i have installed kde ?, … how do i fix?