Upgrading A Yii Application In A Live Environment

We've recently launched our Yii powered application to a client and already we're receiving feedback on improvements and feature requests. As we continue to develop the app the need to upgrade our client to new code with amended database tables / columns will sure enough come so I'm reading around on how-to's.

Any tips or tricks on how to seamlessly upgrade our client & Yii application - I've come across 'migration' and wondered if the community has any ideas?

Thanks in advance.