To update your stream title, you can simply tap the arrow in the upper right corner of your stream, and tap the stream title button.
This will open your stream title options, where you can update your active stream title
On this screen, you can also send push notifications when you update your title. This feature is primarily intended to notify your shop followers and current-stream buyers of important messages, such as when a break has filled and is about to be ripped, when teams have been discounted, and/or why buyers should be in your stream and nowhere else.