incompatible with server

hello everybody i'm a newbie in postgresql

when i do this:
# su - postgre
$ /usr/local/pgsql/bin/postmaster -i -D
/home/postgre/database

i've got this:
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

actually i would like to upgrade my Postgresql,
and i do this to remove older version:
# rpm -e postgresql

than i got this:
error: Failed Dependecies:
postgresql = 7.3.2 is needed by (installed)
postgresql-contrib-7.3.2-3
postgresql = 7.3.2 is needed by (installed)
postgresql-server-7.3.2-3
postgresql = 7.3.2 is needed by (installed)
postgresql-pl-7.3.2-3
postgresql = 7.3.2 is needed by (installed)
postgresql-test-7.3.2-3

can explain and how to fix this
plz, sumbody help me...

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