My reminder checklist for uninstalling Postgres 9.4 beta versions. These instructions assume the use of the Postgres installers provided to the community as a courtesy by EnterpriseDB. For more info, read this answer in StackOverflow.com.
First backup. Use pgAdmin app to select the desired database(s). On each database context-click to choose the Backup command. Go with default options, including "Custom" format which is a strange name for the native binary format. Choosing "Plain Text" creates SQL statements which is interesting but verbose and slow. The only setting you set is to click the button to choose a folder and specify a desired name for the backup file. Include the ".backup" extension yourself. While most Mac apps are built to add an extension, pgAdmin does not.
Run Uninstaller App
In the root folder (not your user home folder), look in Library folder to find the PosgreSQL folder. So that would be: /Library/PostgreSQL/ path. In there find one or more versions of Postgres. Within a version find the app named uninstall-postgresql. Run that app, supply your system password.
Delete Config File
Delete this file:/etc/postgres-reg.ini.
The installer created a Unix user to your Mac named 'postgres'. If eradicating Postgres, you may want to delete that user account. For re-installing a new Beta versions of Postgres, I don't bother. The installer seems to tolerate that extant account.
Check your usual Applications folder. If the PostgreSQL folder remains there, delete it.
Delete pgAdmin Preferences
If you used the pgAdmin app for administering your databases, its preferences file remains. No big deal. I don't know where it lives. Perhaps the Google would tell you.
No Longer Used
In the old days you would delete the file /etc/sysctl.conf. I do not find that file with Postgres 9.4. I suspect the reason is that 9.4 changed dramatically. Previously a Unix setting was needed on your Mac to enlarge shared buffers. Memory for the database cache is now done differently, so that setting is no longer needed. And therefore that configuration file is no longer needed. I have not confirmed this theory, just a guess on my part.