If you don't have a /my-plugins/ directory in your bbpress installaltion, create it on the same level as config.php.
Upload the file into /my-plugins/ directory.
The /my-plugins/ directory needs to be readable and writable by the web server for installation and upgrading or browsers to work.
The plugin browser interface is within the admin area of bbPress, you will need to be logged in as a keymaster.
Further information is on-screen in the browser interface.