Please open a support ticket to email@example.com for DNN site backup. In case the upgrade unsuccessful, We can restore the site with back up files. We will backup your web files and database file, and put them in your backup folder.
Access http://www.codeplex.com/dotnetnuke to download the upgrade package. They are all in releases tab
1) Unzip the DNN upgrade file.
2) rename release.config to web.config
3) Copy Database connection string from old web.configure (there are two connection strings need to be copied)
4) Copy machine keys code from old web.config file, Please copy validationKey and decryptionKey keys
5) Copy "Object Qulifier" from old web.config file
Upload all upgrade files to your web site
Open yourdoamin.com in IE, Your dnn site will start to upgrade.