If you do not already see the email displayed, click on the Show More link under the Activity category under the applicant workflow. Click on the 'edit' link or the 'Email will be sent on...' link and make your changes:
If you want to delete the email, use the Discard button at the bottom left-hand corner of the email form to prevent the email from sending. The system will delete this email from the applicant activity and will not send it in the future. If you simply want to edit the email, make your changes, and then be sure to hit the Schedule button to save your email for sending at your selected time.
Learn how to schedule an email for a later time: How do I schedule an email to send at a later time?