To download the latest version of your software visit: http://updates.gradiencesupport.com/
If you're running a version older than 11.0.1605.10 of Gradience Pro / Enterprise, you [MUST] use Firebird 1.5 as your database engine.
If you are running version 11.0.1605.10 or version 11.0.1606.29, you may use Firebird 1.5 or Firebird 2.0.7. as your database engine.
If you are running version 12, you [MUST] use Firebird 3.0 as your database engine.
Visit https://firebirdsql.org/en/server-packages/ to download FireBird.