Hi Ivy,
Where did you install version 13.x? Did you follow the steps in the linked article? When doing a major upgrade you need to stop the SmarterMail service and uninstall the previous version first; your mail data would not be deleted.
If you're not sure what the steps in the linked article are referring to, it might be that you're receiving SmarterMail as a hosted service and don't actually manage the installation. An upgrade can only be done by someone who has access to the server SmarterMail is installed on.
Andrea Free
SmarterTools Inc.
877-357-6278
www.smartertools.com