To edit your Campaign, hover over the Campaign you'd like to make changes to and then select the "Edit Touches" button that appears. As long as your Campaign doesn’t have any recipients active, you can add touches, delete touches, and change touch-types at your convenience. Edit any content and then click the "Save and Exit" button in the bottom left hand corner.
If your campaign does have recipients active, you can update the content of any touch (think: email subject line and body, call description and talking points, and custom task subject & description). That said, you cannot delete or add new touches. Please also keep in mind if you make any edits to the content of touches while recipients are active, any edits you make won't override custom content you've added for individual recipients or touches sending immediately.