If you select the Microsoft Access database during adTempus installation, you can convert to a SQL Server or MSDE database at any time. All of your adTempus data will be migrated to the new database.
It is not possible to convert from SQL Server or MSDE to Microsoft Access.
To migrate to a new database, run the adtsqldb.exe program found in the "sqlserver" directory under the adTempus program directory, and follow the instructions provided by that program.
For more information on the conversion process and prerequisites, see the Using MSDE or Using SQL Server topic.