If you follow the upgrade process correctly you should not lose any of your previous data.
From the Cumulus readme.txt file:
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Upgrading:
If you are upgrading from a previous version, you can install
this version over the top of these (just run the setup.exe).
Your data files will be saved (you should take backups
before upgrading to be safe).
An upgrade doesn't change or lose any data or settings. You should
of course check everything after the upgrade to make sure all is
still as it was.
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As is mentioned,
ALWAYS backup your data before upgrading. That way if something does go wrong
all you need to do is restore your backup and all is well again.
I recommend closing Cumulus first, backing up your data (backing up the entire Cumulus directory is the simplest way to do this), then run
setup.exe to upgrade.
FWIW, the latest beta version is now 1.9.3 build 1044. Check out the Sandaysoft WIKI, under Announcements and News for what was changed,
fixed, or added.
http://sandaysoft.com/forum/viewtopic.php?f=2&t=7341&start=10