Go into the Evercontact toolbar and then click the "Update" button:
(for Outlook 2007, go to Tools>Evercontact and then click "update".)
If you run into the error message "there is an error with this Windows Installer Package. A program required for this install to complete could not be run" then you'll need to download Microsoft's tool here and then install using that tool.
Once it's downloaded, make sure to close Outlook before installing.