You can update the subject line for any campaign with a draft or scheduled status. Once a campaign is sent however, you will not be able to make any changes.
To change the subject line of your campaign:
1. From the Campaigns Overview page, click the "Continue" or "Edit" button for the campaign you wish to update.
2. Navigate to the design page of the Campaign builder by clicking the “Design” tab at the top of your page.
3. Click the gear icon located on the top right corner of your screen to pull up the Campaign Settings modal.
4. Type the new subject line into the “Subject” field and click the “Close” button:
5. From here, you can either click “Save & Exit” to save your changes, or you can click “Next” to save your changes and choose to immediately send or schedule your campaign.