If you have the required editing rights on the website, you can edit any existing agenda event or event template. You will find the events listed under the main RSVP Events listing of event posts. Templates are listed under a submenu, RSVP Events -> Event Templates.
You would modify the template if you wanted to change the standard organization of roles and notes listed on the agenda. After modifying the template, you can update all the events based on that template.
You would modify an individual event, independent of its template (if any), to change the organization of a specific meeting. For example, you might be doing an all Table Topics meeting with no speakers.
The Roles and Agenda Notes for a specific meeting are represented by colored placeholders on the agenda. Double-click on any of those placeholders for a popup editor dialog that allows you to change the data associated with that role or note.
You can also add additional roles (How to Add Agenda Roles) and agenda notes (How to Add Agenda Notes).
To delete any role or note, click it and then press DELETE on your keyboard.
You can also cut-and-paste or drag-and-drop the colored placeholders to change the order in which the roles and notes appear on the agenda.
See also How to Create a Meeting Agenda / Signup Form From Scratch.