At the time this article was written, changing the database plan in the Tile configuration will not actually change the database plan for scheduler-mysql and scheduler-broker-mysql services in the org system or space scheduler.
If this is still the case, then this needs to be done manually.
The first thing we recommend to do is to take a back-up as explained in this link:
Then, you should be able to upgrade the scheduler db services with "cf update-service", as stated in the MySQL doc below:
cf update-service scheduler-mysql -p "db-medium"
Another option is to delete and re-install the Tile with the new desired db plan and restore the db from the back up previously taken.