Upgrading version
This topic has step by step solutions to common upgrading issues.
Fails during the restart (Windows)
Issue
MSI-based FLS installer fails during the restart step.
Solution
FLS creates a dedicated user to run the application. New versions’ installation may fail during the attempt of application restart.
The reason is in permissions’ conflict between the JetBrainsLS users (see screenshots for reference). It’s likely to happen with build #5374 and older.
To solve the issue, stop and uninstall the application using Windows standard tools of Control Panel + delete related folders from %programData%\ and %userprofile%\. 
After that, repeat the installation of the new version.
Installer fails
Issue
FLS installer fails, but there is no FLS among installed programs, so it can't be uninstalled.
Solution
If there is no the JetBrains License Service in the Programs list, it's very likely it was installed for another system user profile. Old versions had "per-user" type of installation. In this case, you need to find this profile, login and uninstall the application or to clean it up manually from Windows registry. Pay attention that it may be potentially harmful, and we recommend having registry backup.
Logon error
Issue
MSI-based FLS can't be restarted with "Logon error".
Solution
Run the same version MSI installer as it has now and select "Repair" in the wizard.
If you didn't find an answer to your question in this documentation, and you require assistance, feel free to contact the JetBrains Support team.