Luks full disk encryption, how to change passphrase?

If i want to change the passphrase for full disk encryption, how do i do That?

Since i have a Root partition and a swap partition. Do i change both? Where is the Luks header?

I used gnome-disk-utility to change luks password.

At what partition?

which shows LUKS

Yes, but i have 2, root and swap, should i do both?

This is sample.