http://www.phpbb.com/kb/article/transferring-your-board-to-a-new-host-or-domain/Quote:
Purpose
This article explains in-depth how to move your forum from one hosting provider to another (different or same domain) or from one domain to another on the same host. These instructions are only intended to work with MySQL databases.
Requirements
* You will need FTP access to your server. You will also need an FTP client. The client which is used during the course of this article is FileZilla.
* It is highly recommended (although not required) that you have access to phpMyAdmin in order to make a backup of your database. Most hosting providers offer this application. It should be available in the databases section of your hosting control panel (cPanel, Plesk, etc). If you are unsure of how to access phpMyAdmin, you should contact your hosting provider for details.
* For larger databases (greater than 2MB exactly) you will likely be unable to restore the backed up database via phpMyAdmin. Because of this, you will need to use a program called BigDump to restore the database. BigDump can be obtained from here. Instructions will follow on the proper usage of BigDump. Alternatively, you can use SSH to restore the database (details below).
* You will need a basic text editor. For Windows: Notepad++. For OS X, use Text Edit. For GNU/Linux, use GEdit or KEdit depending on your desktop environment. You may also choose to use another text editor of your choice. Do not use a word processor such as Microsoft Word or program such as Adobe Dreamweaver.
* (Optional) If your hosting provider(s) offers SSH (Secure Shell) access to your server, this is the preferred method of backing up and restoring a database. Check with your hosting provider(s) for details. For Windows, you will need an SSH client such as PuTTY. For GNU/Linux and OS X, SSH is built directly into the Terminal.