Want to change database connections from inside psql? You can!
Psql, the REPL for Postgres, has a useful meta-command called \connect, or \c. This lets you establish a new connection to a Postgres server, while closing the current connection.
Here is the required format:
\c or \connect [ dbname [ username ] [ host ] [ port ] ] | conninfo
Only \c [my_database] is required; omitted parameters are taken from the previous connection.