how do I change regional setting for dates?

I live in Guatemala, and our timezone is GMT -6, but my server (postgres 7.1
on a linux redhat 6.2) is storing the dates in the format

2002-07-24 00:00:00-04 ( I this understand represents GMT -4).

My linux servers gives me the the date and time correctly, so I know is not
a matter of the date of the server, and I checked and its GMT-6 (which is
right) .

How do I change the regional setting in postgres?


Thanks,

Ligia