If you're already using phpBB, you can easily upgrade your board by following these instructions:
Make a full backup of all files and database (if you don't do a backup, don't dare to ask for support! )
Did you backup everything? If you didn't make the backup, please, step back to the previous point.
Copy your current config.php and keep it in a safe place.
Check again that your backup is ok and keep it in a safe place.
Login as administrator.
Unpack Icy Phoenix package to one folder on your HD.
Upload install folder to the root of your phpBB forum and launch database_update.php (i.e. http://www.mysite.com/phpbb/install/database_update.php).
Delete install folder.
Remove the following folders (make sure you don't have in those folders some files you may need for some mods you have installed in standard phpBB, but in any case you should have a backup ):
admin
db
includes
language
templates
Remove all files but config.php in your forum root (make sure you don't have some files you may need for some mods you have installed in standard phpBB, but in any case you should have a backup ).
Upload all Icy Phoenix files (all but config.php) in the same folder where phpBB was installed and running. Pay attention that all older files eventually still there must be replaced by new ones.
Apply all permissions listed in Fresh Installation.
Customize what needs to be customized in files and db (some files needs to be edited manually, while most of the options may be set in ACP and CMS).
Unlock your site.
Enjoy your New Icy Phoenix Site .