Every software update means changes in the database schemas. Those changes are a bit tricky to revert. This can only be done by applying SQL statements that revert the previous database migration also done by means of SQL statements and/or migration scripts.
However, in a normal case, you should have a dry run of the system before you start generating any new data. Once you notice that you need a downgrade, you can deinstall the new version and install the previous one as well as use the latest database backup. Indeed, this mean that you need to prepare such backup in advance.