While I was evaluating (using another server and after stopping the current DirSync service) the next version of Azure Active Directory Connect tool in beta, I faced an issue when I switched back to the current DirSync instance: directory synchronization seems to work BUT deleted AD accounts were not deleted on Office 365.
So, I wanted to uninstall the current DirSync instance and reinstall it BUT the ForeFront Identity Manager Synchronization Service component was still installed and there is no way to uninstall it from the Add\Remove Program on Control Panel; it always ask to execute the process as administrator while I was using an enterprise (and local) administrator account
Off course, if I try to install again the DirSync tool, it failed because of this component.
After some digging, I found the correct command to uninstall FIM Synchronization Service – by the way, if you have a media with the full ForeFront Identity Manager product, don’t try to use the installer to uninstall it as it will failed also because of a different version number.
So, the command line to be executed to uninstall the FIM component is msiexec /x {4E67CAD2-D71B-4F06-A7AE-BB49C566BB93}; run this command using a command prompt using the run as administrator.
After a simple prompt to confirm the process, the FIM component coming with DirSync will be uninstalled
After a server reboot, I was able to install again the DirSync tool (version 1.0.7020). Off course, don’t forget to ensure there is no remaining files (like within the SQL directory or Windows Azure Directory Synchronization folders)