Simple check list to upgrade older version of DNN to DNN 4.4.1 or DNN 4.5.0 using shared Hosting... tested on 3 different portals, worked without fail each time.

1. Backup your Database, Backup All Files (in case you need them for recovery).
2. Download the DNN 4.5 UPGRADE.zip files to your local hard disk.  You can get this download on the downloads page here (http://www.dotnetnuke.com/tabid/125/default.aspx).
3. Extract the realse.config file out of the Upgrade .zip file to a location on your hard disk.
4. Download a copy of your portal's existing web.config file to your hard disk.
5. Locally rename your portal's web.config to oldweb.config (or "whatever you want to call it.config").  Locally rename the extracted release.config to web.config (this will be your new web.config file that you will upload along with all the other DNN 4.5.0 Upgrade.zip files.  Now you are prepared to copy the settings from the renamed oldweb.config to the renamed web.config.
6. Open web.config and oldweb.config in Text Editor editor of your choice (VS2005 preferred).
7. Copy "SiteSqlServer" line under <connectionStrings> from old to new.
8. Copy "SiteSqlServer" line under <appSettings> from old to new.
9. Copy "InstallationDate" line under <appSettings> from old to new.
10. Copy "machineKey" line under <system.web> from old to new.
11. Save your work in the web.config file that you have just altered, and place the web.config file back together with the other files in the DNN 4.05.00 UPGRADE.ZIP file... Delete the release.config file if it still exists among the other zipped files in the 4.5.0 Upgrade.zip file folder... and get ready to now simply upload all of the files from the DNN 4.5.0 UPGRADE.ZIP file to your portal's root directory
12. Before you upload all your files from the DNN 4.5.0 Upgrade.zip, you can place an app_offline.htm file with your own custom message in your DNN root directory to prevent users from accessing your site during upgrade process; instead they will see the text from your app_offline.htm file...
13. Copy files from DNN 4.5 installation zip over current installation (overright if file exists) in your DNN site's root directory.
14. Browse to the web site, it will automatically upgrade.

Use the instructions at your own risk...  But know that I have used this process several times without fail.  Still, that does not guarantee your success, but you shouldn't have any problems.

Parts of these instructions were borrowed from Nina.  I just felt that a good number of novice users would appreciate a bit more detail in the forums.

Please let me know if this has been helpful!