What contains the configuration changes made in an instance (i.e. changes in a form) and helps to implement the changes from the Dev environment to another environment?

Import sets are used to import data from external sources into a ServiceNow instance, not to migrate configuration changes.

Update sets capture configuration changes, such as new forms, fields, scripts, and business rules, made within a ServiceNow instance, allowing these changes to be migrated from a development environment to testing or production instances.

Transform maps define relationships between fields in an import set table and fields in a target table, used for data transformation during imports.

System dictionaries define the properties of fields and tables within a ServiceNow instance, but do not themselves contain or transfer configuration changes.