This article applies to Classic Commerce. (Looking for Contextual Commerce documentation?)
To offer free updates on a product, go to SpringBoard's Store Home » Products and Pages. Select your product. For the File Fulfillment, click Edit. Under Download Version Behavior, select Newest File Version. Click Save.
If customers have already downloaded a previous version of your product (and their download link expired due to reaching the maximum number of download attempts or to exceeding their allotted download days), their download link will now be automatically reset with a new time expiration and download attempt count, allowing them to download your updated file(s).