Before migrating to a greater version of your DB please upgrade your version on the DB test server and run some test with Appeon to try to connect to the DB. If there is no problem you can upgrade the product database server.

For the Appeon Developer, you don't need to change the configuration of the DB setting. You don't need to re-deploy it if the configuration is changed while re-deploying the application. However you need to change the configuration if the DB type is changed.

In the AEM you need to change the Database Host. In case you have changed the Database Port/Name you need to do the same changes in AEM.

If MSSQL 2012 cannot be connected in AEM, please try to see if it is connected successfully in PB with OLE Microsoft OLE DB driver, if yes, this issue should be caused by the error port number of MSSQL 2012 , thus you can refer to the attached file to solve this issue.