Open a support ticket to schedule the upgrade from MariaDB 10.0 to 10.2 or 10.2 to 10.3 or 10.4. In the ticket detail the date and time when you want the DB upgraded. The support team needs 48 hours’ notice and the merchants dev team needs to be available. Once the time and date are agreed for the upgrade, do the following:
Put your site into maintenance mode, and stop any DB activities, e.g., crons.
The Adobe Commerce support team will begin the MariaDB upgrade process. If all the above steps have been taken, and the database is average size, this can be done in about an hour. Larger DBs will take longer. You will be informed via your ticket once the upgrade is complete.