User Control Panel - Profile - Edit Account Settings
That's how.
Do you probably need a picture? No problem! I took these screen shots for you to see..
Follow my lead (the one that is encircled red that's what you should click.)
USER CONTROL PANEL: (click on the spoiler)
PROFILE: (click on the spoiler)
EDIT ACCOUNT SETTINGS: (click on the spoiler)
And this is how it's done: (again click on the spoiler.)
Your welcome.

By the way, the account you are using for SM changes the password when you change it at the stated instructions.