When you're installing Symphony for the first time, you have to tell it what URL you're going to be using to access the site. They strongly encourage you to NOT change it once it's decided on, but I had to change it today. You see, the site that I built is very lacking on the backend features, and I wanted to use Symphony on the main site. It's not easy, but it is pretty simple, as far as I can tell.
Step 1: Move the files
The only thing you really need to do is access your server, either via ftp or a shell, like I prefer. Then move the directory where you installed Symphony to the new directory. I wanted to save my old files, so I put them in an archive directory.
$ mv zastica.com archive/zastica.com
$ mv symphony.zastica.com zastica.com
Step 2: Change the settings
Symphony will fail if you do only that because it requires a number of files based off of the setting you gave it when you first installed Symphony. Luckily, those settings are in one place—manifest/config.php—and they're the first two lines of code. All you have to do is change the paths to match what they are going to be now.
$ pico mainfest/config.php
This is what that looks like:
<?php
define('DOCROOT', '/home/****/symphony.zastica.com');
define('DOMAIN', 'symphony.zastica.com');
. . .
All I needed to do was change symphony.zastica.com to zastica.com in the first case, and www.zastica.com in the second. Voila!