Frequently Asked Question

First check what postgis versions are available:

postgres=> select * from pg_available_extensions WHERE name = 'postgis';
  name   | default_version | installed_version |                          comment                           
---------+-----------------+-------------------+------------------------------------------------------------
 postgis | 3.1.4           | 3.0.2             | PostGIS geometry and geography spatial types and functions
(1 row)

If you want to use that "default_version" that gets listed, then create a new database. It will have that version of the extension. You can dump the contents of your old database and import the data into the new database.