Installing harmon.ie version 4.0 on top of a previous version will upgrade the installation.
To upgrade the sidebar for IBM Notes 9 / 8.x:
Download harmon.ie plug-in NSF file.
Copy the NSF file to the IBM Notes local application folder. The path to the local application folder can be retrieved by selecting File > Preferences in IBM Notes and clicking the Basic Notes Client Configuration node. The path to where the NSF file should be copied is listed as Local application folder.
Open the plug-in NSF file from the File > Open > IBM Notes Application application menu in IBM Notes and follow instructions provided by the installation wizard.