To change your password on Facebook if you're already logged in:
Click in the top right of Facebook.
Select Settings & Privacy, then click Settings.
Click Security and Login.
Click Edit next to Change password.
Enter your current password and new password.
Click Save Changes.
If you're logged in but have forgotten your password, follow the steps under Change Your Password then click Forgot your password? and follow the steps to reset it. Keep in mind that you'll need access to the email associated with your account.
Reset Your Password
To reset your password if you're not logged in to Facebook: