To change password as Master Admin in new QuickBooks Online:
From the home page screen

• Select the Company “Gear’ (upper right corner)
• Go to “Your Company” and “select “Your Account”
• Choose “Personal Info” under “Your Account” heading and click “Edit Personal Info” blue button
• Scroll-down bit and find “Sign-In Info” heading
• “Change Password” link is just next on the right side
• Click “Change Password” link; new “Change Your Password” screen will open. Provide asked information and save