Be sure to also read Important Upgrade Information and Preparing to Upgrade.
WARNING: If you are currently running ListManager, DO NOT upgrade your existing (production) ListManager server until you are certain you want to upgrade. You WILL NOT be able to downgrade it to an earlier version.
There are two ways to test ListManager:
1. Test a clean installation on a test server. (Required for MSDE databases; strongly recommended for other databases.)
2. Test your production data on a test server. (Not permitted for MSDE databases.)
We strongly recommend the first option: that you test a clean installation of ListManager on a test server. If you test using your production data, be aware that if you run the test server and the production server simultaneously, you run the risk of having duplicate messages sent unless you follow these instructions carefully.
More
1. Important Upgrade Information
3. Testing Production Data on a Test Server
3. Upgrading ListManager from 4.2 .1
4. Upgrading ListManager 5.0 or Higher
5. After Upgrading ListManager