I am updating from EventSentry v2.43 to the latest version which has a

Starting with version 2.50, EventSentry uses a new database layout. Depending on your circumstances you can either choose to start over with a new database, while still having access to your existing (old) database, or migrate the data from the existing to the new database.

When updating to EventSentry v2.50 or later you should follow these steps:

Run the setup. When using Microsoft SQL Server then the installer can setup the new database for you automatically during installation. Otherwise you can launch the "Database Setup Wizard" after EventSentry was installed.
When using MySQL or Oracle, run the Database Setup Wizard which is located in the EventSentry start menu folder. Be sure to create a database and system DSN pointing to the new database before starting the wizard.
If you need to migrate your data then launch the Database Migration Wizard which is located in the EventSentry start menu folder. Be sure to create a system DSN pointing to the new database before starting the wizard.
Setup the new web reports. When using IIS this can be done during the installation with the MSI installer. Otherwise copy the new files to a directory served by your web server, more information can be found in the manual.
It is recommended that you reconfigure your ODBC target(s) to use connection strings instead of System DSN names, especially when using MS SQL Server or Access. This will ease the deployment of EventSentry since you won't have to setup DSN names on the monitored machines anymore.
Update the agents and configuration on the remote machines using remote update.

Please see the manual and the additional links for more information.