You can edit your outgoing campaign email content anytime. Select Content and press the edit button by the contact group. Pick the content group you want to edit. Then, select preview for the email you want to edit. Click Edit to make changes.
Use the check box to apply changes that you make to all 4 templates for that contact group. Be careful though, typically the opening and closing are different for all 4 template so if you click the box for the opening and closing you may overwrite the different openings and closing. Typically the attention statement and benefit statements are the same.
When you make a change to your content, the updated content will be used the next time that template is used to create a campaign email.