After you have created a promotion, you can edit the same whenever required.
To edit a promotion
Go to ADMIN SETUP> Pricing Administration > Promotions. The Promotions page is displayed.
Search for the promotion you want to edit.
Click the promotion name. The Summary screen is displayed.
You can expand each section to see the details.
Click Edit to modify the expanded section. For example, expandBenefits section for a promotion and clickEdit to modify the benefits that are applied to the selected promotion.