Update liquibase instructions

Author: NicolasCwy

maintainer-guide.md

@@ -153,16 +153,17 @@ Since the detail of such vulnerability cannot be disclosed until it is fixed, an
 The complete details can be filled in just before merging and/or after the fix is deployed.
 
 ### Schema migration
-Schema migration is necessary when tables/ columns have to be added 
+Schema migration is necessary when tables/ columns are amended/ added. Refer to TEAMMATES repo [docs/schema-migration.md](https://github.com/TEAMMATES/teammates/tree/master/docs/schema-migration.md)
 
 **Role: RL**
-* Consolidate all changelogs in the current release folder in `src/main/resources/db/changelog` into a single changelog to put into `src/main/resources/db/changelog`
+* Follow dev guide to create new changelog with name `db.changelog-<release_number>.xml`. The previous release is the base and the new release is the target branch.
+* Ensure new changelog is in `src/main/resources/db/changelog` and add it as the last entry in `src/main/resources/db/changelog/db.changelog-root.xml`
 * Follow dev guide on targeting changelog created and run `./gradlew liquibaseTag -PliquibaseCommandValue=<release-num>` to tag changelog to current release
-* Create new folder in `src/main/resources/db/changelog` with the next version as file name
+* Notify PM of schema change for them to run on production database.
 
 **Role: PM**
-* In `gradle.properties` amend the fields `liquibaseDbUrl`,  `liquibaseUsername` and `liquibasePassword` to match the IP and the username and password for the role used to login to the Cloud SQL
-* Run `./gradlew liquibaseTag -PliquibaseCommandValue=<release-num>`
+* In `gradle.properties` amend the fields `liquibaseDbUrl`,  `liquibaseUsername` and `liquibasePassword` to match the IP and the username and password for the role used to login into Cloud SQL
+* Run `./gradlew liquibaseUpdateToTagSql -PliquibaseCommandValue=<release-num>`
 
 ### Data migration