Migrate data from PostgreSQL9 to 14

1. What is the issue? Please be detailed.
I am trying to build a fresh and updated install of ODK Central in a Google Cloud VM using a Cloud SQL PostgreSQL14 as database. We have an old ODK central in a separate VM utilizing also a Cloud SQL PostgreSQL9. I want to be able to migrate our data from 9 to 14, or from the old instance to the new instance. I am also exploring on using Cloud Storage to handle media files. May I get some tips on how might I be able to do it?

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Have you checked out the upgrade docs for v2023.2? That was the upgrade that moved PostgreSQL database from v9.6 to v14. Step 8 includes tips for upgrading a custom database.