To update your domain email settings within gmail, you can do this quickly by accessing the settings pages within your gmail account you can find current step by step instructions for your desktop/laptop, android or iphone/ipad by visitng the Gmail help centre here:
https://support.google.com/mail/answer/6562
For SSL customers, you can find step by step instruction from a desktop here: PDF
I really like this and it helps me more to update my domain email settings within Gmail, I can do this quickly by accessing the settings pages, very thankful for this.