The .NET updates, Application Request Routing module, URL Rewrite module, etc are all packaged in the installer and so should be deployed when upgrading. Because 8664 isn't that far behind, there isn't anything too specific to watch out for and your upgrade will look like this after you get a full backup: 

1. Stop the SmarterMail IIS site and application pool.

2. Stop the SmarterMail system service. 

3. Note the current install directory, then uninstall SmarterMail b8664.

4. Install the new version of SmarterMail to the same install directory used previously. 

5. While the installer is copying new files; go ahead and start the SmarterMail application pool and IIS site. 

If you do run into any errors or other failures a good place to start looking for clues is the installer log we generate if the install fails, and the Event Viewer in Windows where you can filter the Application and System log types to Critical/Error/Warning. The components we're deploying are ultimately Windows components, so any trouble there should be logged in the Windows logging and will get you pointed in the right direction. I hope that helps!