Changing column data type on an existing table

Hi,

I have an app that I released with a particular field
as varchar 255.

Can someone give me a script example I can use to make
an upgrade script to change it to text or at least to
larger varchar without losing existing data?

I support 3 different dbs in my app, Postgre is the
newest and least familiar to me but I am trying to
learn.

Any help much appreciated.

Joe Audette

joe_audette [at] yahoo dotcom
http://www.joeaudette.com
http://www.mojoportal.com