If you are unable to login to your account, you want to reset your password using the steps above.
If you are able to login to your account and want to change your password, you can do so by selecting your profile name/image from the "My Account" link.
Once in your profile, click on the 'Edit Profile' button on the right side of the screen.
On the first tab to the left (Manage Account), expand the section titled : 'Manage Password'
You will then be prompted to enter your current password as well as your new password (and password confirmation).
Hitting the "Change Password" button will then save your new password.