by WhiteRider » Sun Aug 12, 2012 4:22 pm
It depends on your current setup - if you already have a lower version of 9.0.x you can just run the latest 9.0.x installer.
If you have an older version of PostgreSQL (8.3 or 8.4) and want to convert your existing databases you will need to make a backup using the old service (via the menu File > Backup). Then you can install the new version (9.0) - I'd suggest specifying a different port when you install 9.0 (maybe 5490 instead of 5432) so that you can use either service just by changing the port you use when creating a database.
Once you've installed 9.0 run PT4 and create a new database specifying the new port number to connect to the 9.0 service, then use File > Restore to restore your existing database to the new service.