Are you installing from One-Click Installs or by yourself?
If you install from One-Click Installs, you will need to specify a directory where you want to install to. For example:
Install to: http://www.yourdomain.com/phpbb
PHPBB will be installed to /home/username/yourdomain.com/phpbb directory where you can access via http://www.yourdomain.com/phpbb
If you already installed it via One-Click Installs, you DO NOT need to upload it again. It will be automatically installed in your specified directory.
Btw, if you want to host any files, they must go into "yourdomain.com" folder. If you upload them outside this folder like /home/username/phpbb, they are not available to public.
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