At this time, there is not a system in place for generating and sending notifications to guests regarding updates you make to your wedding website. This is a very popular request and is something we might be working on for future improvements.
In the meantime, you are welcome to take advantage of the "Email Guests" feature included with your MyWedding account. This feature allows you to compose and send messages to your guests directly from your account. You might consider sending a message to your guests when you make an update. The message will contain a direct link to your website that they can follow from the email message.
Furthermore, you can save a message - including the list of previous recipients - and send the message again without having to compose it all over again.