Once you are logged into your account click the 'Settings' n the top right that looks like a gear icon and choose 'Login info' under 'Account settings'. Enter your new password and confirm it again and save settings. Be sure your password is alphanumeric characters (combination of letters, numbers and special characters)
Click 'Save' once you are done.
That's it! your password is set. That was easy wasn't it? Let us know if you have any other questions.