Well, the password part is easy, but Bodhi currently does not have a GUI for that so you need terminology.
After typing this command it will ask for your existing password,
Next it asks for the new password,
Next it asks you to confirm the new password.
Resulting in a friendly message that your password is updated.
In theory changing the username is also a simple command, BUT
After the change you need to change the name of your home folder using another command and you should realize that you probably have lots of stuff on your machine that refers to the old username and those don't get updated. Like bookmarks, just to name an example. Think about it. When you really want to do this there are nice methods though they involve some more then just a command in terminal.