Dump existing data:
python3 .\manage.py dumpdata --indent 2 --natural-primary --natural-foreign -o dump.json
[...........................................................................]
Change settings.py to Postgres backend.
Make sure you can connect on PostgreSQL. Then:
python3 .\manage.py migrate --run-syncdb
Finally:
python3 .\manage.py loaddata dump.json -i
Installed 420 object(s) from 1 fixture(s)