I created a system that works for us for Change Orders. There may be a different way, but this is the easiest way I've found to update projects.
I go to the estimate associated with the project, and add a task. Typically I select "Service". If you know a way to add a specific task I would love to know because I need one that says Change Order.
In the description I add "Change Order" and then type the additional work proposed. I update the cost, and save it. This updates the estimate, and allows me to forward it to the customer so that they are notified.
I made an example to show:
Like I mentioned I'd love to be able to modify the task name, but I haven't found a way to do that yet.
Hope this helps!