Brainshark can't be used to edit uploaded content (i.e. text on slides) or create new content from scratch. Any content that needs to be added or modified will need to be created outside of Brainshark (for instance, in PowerPoint) and then added or replaced into Brainshark.
In Brainshark, you can choose the "Replace PowerPoint Slides" option when adding slides to your presentation in order to replace existing content with updated content (and maintain any audio recordings).
If you need additional assistance, please contact Support.