in short: mind the DNN Platform Suggested Upgrade Path.
- Make a copy of your SQL Database to the SQL Server in your testing environment.
- Copy the Files from your (DNN) website to the root of a website in your testing environment.
- Change the HttpAlias in the PortalAlias table to the host header from this testing website.
- Change the connection string in the web.config in your testing website to the copied database.
- Check permissions (database, file system)
- Check if everything is running.
- Backup the database and files from your testing environment.
- Upgrade the website in your testing environment. See DNN Platform Upgrades for details.
- Check if everything is running. If you need to update any extension you can do the following:
- Unzip the DNN upgrade package to an empty folder on your machine (e.g. C:\DNN_09.11.00_Custom)
- Copy the extension upgrade package(s) to the approbriate folder under the /Install folder (Module, Skin, Provider, Language...)
- Zip the complete folder (C:\DNN_09.11.00_Custom) to a new DNN upgrade package.
- Restore files and database from the previous version (Backups from step 7)
- Re-run the upgrade and test.
- If everything works, go to step 7 until you are on the latest version.
- When you are on the latest version, repeat the upgrade steps (using the customized packages if necessary) in your production environment - not after backing up everything, but this is the only backup you need this time. Take the site offline as described here: DNN Platform Upgrades
Hope it helps.