Cygwin-Postgres - The data directory was initialized by PostgreSQL version 7.2

I'm running under a Cygwin window, on a Windows XP operating systems, 256
MB ram, 1Ghz Intel processor, with over 4GB free disk space on my local
drive.

How do I painlessly upgrade my database from 7.2 up to 7.3?

Thanks in advance,
-Martin

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$ postmaster -D /usr/share/postgresql/data/ &
[2] 2092

hurstm2(at)HURST-MARTI36 /
$ FATAL: The data directory was initialized by PostgreSQL version 7.2,
which is
not compatible with this version 7.3.

[2]+ Exit 1 postmaster -D /usr/share/postgresql/data/
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