Two Versions of PostgreSQL Installed - How to uninstall one particular version

Hi,

I got this error:
"-bash-2.05b$ /usr/local/pgsql/bin/pg_ctl start
server starting
-bash-2.05b$ FATAL:  database files are incompatible with server
DETAIL:  The data directory was initialized by PostgreSQL version 7.3, which is not compatible with this version
8.3.8."

I think I must have two versions of Postgres installed.  How do I uninstall the 7.3 version?  Do I need to do a manual
uninstallby removing Postgres related files from /usr/bin and etc?  Or is there an automatic way?  The problem is that
I'munclear what files need to be removed.  I think might also need to delete a file in the /etc/init.d directory. 

I'm running on RHEL 3.9.

Thanks
Mary