General

These instructions apply to v 2.0 or later.

Steps to add a new DB version\changes to the existing database

Open \application\config\version.php and raise the $dbversion variable by one. So if it 155 make it 156.
Open each file in \installer\sql and add the necessary changes. Make sure the changes are consistent across all three files. Pay attention to the database specific field types (check out other tables for comparison/examples). Important: If you need to use field type 'text' then make it 'varchar(max)' in MSSQL.
In each file in \installer\sql edit the last SQL statement in each to reflect the new dbversion number.
Open \application\helpers\update\updatedb_helper and in the end of the function db_upgrade_all() add a new condition block that does the necessary updates to the database scheme of the previous version. If you are using the proper functions the changes will be cross-DB compatible - check out how it is done in previous conditional blocks.